Barker took to the task of drafting the separation documents with some alacrity. The prime minister, determined not to allow the British to intervene in the negotiations with Malaysia, wanted it to be a closely held secret. The Singapore Attorney-General (known as State Advocate-General during merger) would normally have been the one tasked to draft legal documents for the government. But Barker feared he would have to involve a few of his junior staff and the news would eventually leak. He thus took it upon himself to research the issue and to draft the papers himself.

He found a legal precedent in his first search at the law library of the University of Singapore. The British West Indies Act 1962 had been passed three years earlier to bring about the break-up of the West Indies Federation.

Barker determined that since the Malaysian constitution did not provide for states to secede, he would have to draft a constitutional amendment in addition to an agreement to separate. He structured the separation papers into three documents: an agreement relating to the separation of Singapore from Malaysia as an independent and sovereign state, with two annexures - a proclamation on Singapore by the prime minister of Malaysia, and a bill to amend the Constitution of Malaysia and the Malaysia Act.

Both governments would sign the agreement, following which the Malaysian Parliament would have to pass the constitutional amendment bill providing for Singapore to leave Malaysia.

Barker also drafted a Proclamation of Singapore for Prime Minister Lee to issue... He finished the first drafts in "three or four days" and circulated them to the prime minister, Goh Keng Swee and Stanley Stewart, the head of the Singapore civil service. They made some amendments and by the end of July, the drafts were ready for Goh to show the Malaysians.

Goh showed Razak the drafts on 3 August 1965. On his return to Singapore that afternoon, he went to Barker's office in City Hall and called Lee, who was on his annual family vacation in Cameron Highlands, to report that the Tunku had agreed to Singapore's separation from the federation.

Goh spoke in Mandarin to prevent the Malaysian telephone operators from eavesdropping. He and Barker then spent the afternoon discussing the changes the Malaysians wanted to make to Barker's drafts before one final meeting in Kuala Lumpur.

It would appear that Lee, who stayed on in Cameron Highlands a couple more days to maintain cover, called Barker later that night or the next day, only to be frustrated by a bad connection and Barker's failure to recognise his voice. Unable to engage in a more substantive discussion over the phone, they apparently discussed their travel plans.

While Goh took the train to Kuala Lumpur on the night of 5 August and Lee quietly left Cameron Highlands by car the morning of 6 August, Barker flew into the Malaysian capital that morning. The three men met in Temasek House (which is now the official residence of the Singapore High Commissioner to Malaysia) for Lee to sign off on Barker's latest drafts, and Goh and Barker then adjourned to Razak's office at 4 pm that afternoon.

Nine hours and a change of venue later, Singapore was out of Malaysia.

In Barker's account of those 20 days leading up to 9 August 1965, he gave the impression that his role was limited to the drafting of the legal documents. Lee did not want the Malaysian Attorney-General to draft the papers, Barker confided in Malaysian lawyer Tommy Thomas. The lawyer in Lee knew that if his side did the first draft, he would be able to set the parameters for the negotiations. And fortunately for Singapore, then Malaysian AG Kadir Yusoff was happy for Barker to do the work.

In his oral history interview, Barker paid tribute to Goh Keng Swee as "the architect of the separation". He would likely have been proud to be called the draughtsman. He was not involved in the political decision-making, just the legal drafting, he liked to tell those who asked about his part. But without Eddie Barker at the last meeting alongside Goh Keng Swee, things might have gone a little differently.

'WE WERE PUTTING OUR NECKS OUT'

Goh Keng Swee kept a file he code-named Albatross, for how "the great expectations that we foolishly had - that Malaysia would bring prosperity, common market, peace, harmony... became an Albatross round our necks".

He wrote notes of his meetings with Razak as well as his personal concerns about the talks in an elegant cursive script. They make clear that he saw Barker's participation as crucial for a successful outcome at that last meeting in Kuala Lumpur. Goh also recorded that he told Razak that Barker was among the very small group of Singapore leaders privy to the discussions on secession from the beginning. It probably felt good for Goh to be able to share the burden with Barker. After the prime minister circulated his memorandum on constitutional re-arrangements to the Singapore Cabinet, Goh had worked with Lee to negotiate "a looser form of federation" with the Tunku, only to be stymied by the British. As Barker described it: "... their officials would go round, say, to the Minister for Home Affairs, then say, 'How can you let the Singapore Government be in charge of the Police?' And then tell the Minister for Communications, 'How can you let the port (both the airport and the seaport) be run by them?' Now this sort of thing went round and that was the end of this proposal for a looser form of federation."

It was Goh who rather inadvertently started the ball rolling again. On 13 July 1965, following the massive rally by the Malaysian Solidarity Convention in June, Razak invited Goh to "the usual bellyaching session against Lee" at his home in Kuala Lumpur. Telling Goh "we can't go on like this", Razak asked him for ideas. A surprised Goh suggested "the best thing would be to call it quits; we should go our separate ways". Razak, sceptical Lee would agree, asked Goh to sound out his prime minister.

Goh received approval from Lee to proceed, and went back to see Razak on 20 July. Lee discovered almost 30 years later that Goh "never pressed Razak for a looser rearrangement as I had asked him to". Instead, Goh "went along with their desire to have us hive off ".

BARKER'S ROLE

Barker always maintained even in private that he "had no role in the politics of the separation or in the political decision-making". Goh's notes suggested otherwise. He also knew that Barker's involvement would reassure the Malaysians, for both the Tunku and Razak trusted Barker. Indeed, Goh, Lim Kim San and Barker were perhaps the least politically active members of the Singapore Cabinet, and thus, looked on favourably by the Malaysian leaders...

By his fourth meeting with Razak on 3 August, Goh had secured Tunku's acceptance of the plan for Singapore's independence; to use his chess metaphor, it was "a won game". Goh felt his own role was now over.

It was up to Barker to convince the Malaysians that the documents he had drafted looked after their interests too, and in this matter of mutually desired separation, there was no need for caveat emptor. For of course, Singapore was not about to give in to all of Malaysia's demands, nor could it limp on under the existing circumstances. Razak told Goh that the Tunku had two conditions for separation: Singapore was to make an adequate military contribution to Malaysia's and Singapore's defence, and enter into a Defence Agreement with Malaysia; and no treaty was to be entered into that would contravene the objectives of that agreement...

Goh then proposed that he and Barker return to Kuala Lumpur with a new draft after the Tunku's return from London on 4 August. If all went well, they could sign the documents and present them to the Federal Parliament when it reconvened on 9 August. Goh scheduled the last meeting with Razak for the afternoon of 6 August. In his notes, he wrote: "And I knew that at that meeting, Barker would be the principal actor on our side. In fact, my role was over. My role as a negotiator was to get the Malay leaders into a mood in which they will accept the Separation Agreement with the minimum fuss and bother, particularly to avoid matters of defence which Razak raised and to gloss over them, never to get entangled on these issues which might get the whole thing unstuck. And when they appeared hesitant and unwilling - as Razak from time to time gets into this kind of mood - we tell them that they will be the worse off for it and they better make up their minds quickly. But having said that, I must say that that's only so far as I am concerned.

"So far as the PM was concerned, his troubles then began, because he had to convince other colleagues to go along with it. Well, that's his job, not mine. And so far as the drafting and discussions of the actual text of the Agreement, well, Mr Eddie Barker had to do that."

Both men were nervous going into that last meeting as Malaysian nationals. Barker remembered Goh telling him before they went into Razak's office that "we got to be careful". His legal training told him that what they were doing could be considered treason and the Malaysians could use the documents he had drafted as evidence and "locked us up as traitors".

Although he considered their Malaysian interlocutors old friends from his Raffles College days, Barker said that both he and Goh were well aware that "he and I were putting our necks out".

They were also about to start the meeting with a lie; Lee Kuan Yew was already in Kuala Lumpur, but a plank of their negotiation strategy was to pretend he was still in the Cameron Highlands so that he would not be forced to come to the table too. Lee's presence would have changed the personal dynamics, the Malaysian animus towards him being such that they were likely to harden positions as soon as he objected to anything.

With Barker and Goh, the Malaysian negotiators were "friendly; serious but friendly". And as determined.

Recalled Barker: "We were determined to get out. I think they were just as determined that we should go. It was not a question of them kicking us out, it was an agreement to separate. But there was no going back. It was just, 'Alright, we agree to separate,' and that's the best we could have done then. There were no second thoughts. We just discussed separation, the draft, a few amendments, and that was it. We signed soon thereafter."

Barker was the first to sign the separation agreement after the Malaysians. They had been waiting hours for first Razak's typist, who was not used to legal documents and made too many mistakes, then Lee's secretary summoned from Temasek House, Teo Ban Hock, to finish typing the documents. It was past midnight when Teo was done; they had been at it for more than five hours.

The five Malaysian negotiators signed their names to the separation agreement without reading it. In what the careful lawyer in him immediately regretted as a reckless act, Barker allowed Razak to pressure him into also signing the agreement without reading through it.

Friendship, he knew, cut both ways. Just as Razak had accepted his word that Lee would sign the agreement, Razak expected Barker to take the same risk as him. So Barker signed happily, but "buta" (blindly). Yet, he still had the presence of mind to maintain some semblance of protocol: after the names of Prime Minister Lee Kuan Yew, Deputy Prime Minister Toh Chin Chye and Goh Keng Swee, his was the fourth on the agreement setting Singapore free as an independent nation.

In his memoirs, The Singapore Story, Lee recounted what Barker told him of that moment: "Eddie said they had all got drunk while waiting, and when the documents were finally ready, he was the only one sober enough to want to read them before he signed. Razak, who liked Eddie from their hockey-playing days in Raffles College, said, 'Eddie, it's your draft, it's your chap who typed the final document, so what are you reading it for?' So Eddie, too, signed without further ado - 'sign buta' (signing blindly), as he told me in Malay. Keng Swee was so soused that he had gone straight to bed. But Eddie went through the documents, was greatly relieved to find no mistakes, then handed them to me. After I had quickly scanned the amendments myself, I looked at Eddie and said, 'Thanks, Eddie, we've pulled off a bloodless coup.' "

• The author Susan Sim is an Adjunct Senior Fellow at the S. Rajaratnam School of International Studies, and a former Singapore diplomat and journalist. Her book has just been released.

Correction note: An earlier version of the story said that by Dec 27, 1974, Tunku Abdul Rahman was suggesting to Goh Keng Swee that Singapore should "hive off". The correct year is 1964.