In his foreword to a new book on the 30-year dispute, Minister Mentor Lee Kuan Yew disclosed he had instructed that the materials be shown to Malaysia, 'an unprecedented unilateral move'.

On Friday, Chief Justice Chan Sek Keong took up the point in his keynote address at the launch of the book Pedra Branca: The Road to the World Court.

He said: 'I am not sure whether the International Court of Justice (ICJ) realised that most of the documents used by Malaysia in her arguments against Singapore were produced by us.'

'So, you can imagine our deep disappointment when it was alleged that Singapore had withheld from the court a letter which Malaysia believed would damage our case.

'The truth is that we had gone round the world looking for it for some 30 years without success,' he added.

This move and other previously-undisclosed facts about the Pedra Branca case are contained in the 190-page book on how both countries managed the dispute, which the ICJ resolved in May this year.

Pedra Branca, a football field-sized island at the eastern entrance of the Singapore Strait, was first occupied in 1847 by the British, who built Horsburgh Lighthouse there.

Singapore later took over, and Malaysia staked its claim in 1979.

In May, the ICJ ruled that Pedra Branca belonged to Singapore, and that nearby Middle Rocks belonged to Malaysia.

Who owns a third maritime feature, South Ledge, is being worked out by the two countries. The ICJ says it belongs to the country in whose waters it sits.

The long journey to the ICJ resolution was highlighted by Deputy Prime Minister S.Jayakumar, who co-wrote the book with Ambassador-at-Large Tommy Koh.

Speaking at its launch at the Ministry of Foreign Affairs, he said: 'For both of us, working on the case for some 30 years was really a labour of love'.

Read the full story in Saturday's edition of The Straits Times.