British Prime Minister Theresa May has singled out Singapore alongside Australia, India, Mexico and South Korea as potential top trading partner nations for her country once it leaves the European Union.

Addressing Parliament in London after Britain and Australia launched preliminary discussions this week about a new trade deal, Mrs May pledged that the United Kingdom will become the "global leader in free trade".

But her bullish remarks were soon overshadowed by a clarification from Australian trade minister Steve Ciobo, who pointed out that no trade deal was feasible until Britain actually leaves the EU. Yet no concrete timetable for that exists, since British ministers continue to squabble over how and when the process of separation from the EU should begin.

Mrs May, who came to power in July in the wake of Britain's referendum decision to leave the EU, has steadfastly avoided saying anything meaningful about the topic; her standard response to media questions on the matter is that "Brexit means Brexit", a slogan merely designed to indicate that she intends to respect the referendum's outcome, without revealing what Britain's negotiating tactics with Europe would be.

Mrs May's determination to retain the air of mystery was reinforced this week by her announcement that she reserves for herself the decision on when to start the "divorce" talks with the EU, without giving MPs a formal say on the matter, and that, until she does so, she has no intention of providing "a running commentary on every twist and turn of the negotiations".

She can afford to wait, largely because the British economy still appears largely unaffected by the prospect of the country leaving the EU. Economic growth for the year is estimated at 0.6 per cent, and a lower currency has boosted tourism and retail sales. "We have had some good figures and better figures than some had predicted would be the case," Mrs May told her Group of 20 counterparts during the recent summit in China.

Still, as Bank of England governor Mark Carney admitted to a parliamentary committee in London this week, the UK economy is currently growing at half the pace of the three months before the EU referendum vote. And data just released by Britain's Office for National Statistics indicates that manufacturing output is declining sharply, as British factories cut back production as a result of the Brexit uncertainty.

So, time is not on Mrs May's side.

But the Prime Minister's bigger problem is that the debate about what Brexit should mean is now shifting inside her own ruling Conservative Party. In the immediate aftermath of the shock referendum result, most Conservative MPs appeared to agree that Britain's biggest objective should be to maintain access to the EU single market.

Now, however, the prevailing opinion among legislators is that stopping European immigration by re-imposing border controls on EU citizens should be Britain's key objective, even if this means sacrificing the benefits of trade.

"We will decide our borders, our laws and taxpayers' money," said Mr David Davis, the newly appointed minister in charge of the EU withdrawal negotiations, who also claimed that it was "very improbable" that the UK could remain a full member of the EU's trade zone.

The British Prime Minister's spokesman was quick to distance Mrs May from these remarks, insisting that the minister was giving his "personal opinion rather than outlining government policy".

Still, the danger that trade may be sacrificed in a debate about immigration proved alarming enough for the Japanese government, which released a 15-page memo making it clear that Japanese companies expect the government in London to maintain the country's unrestricted access to EU markets if it still wants to attract Japanese funds. Japanese companies direct half of their European-bound investment through the UK and are responsible for creating more than 140,000 British jobs.

Privately, officials close to the British leader welcome the publication of the Japanese memorandum, for it strengthens Mrs May's arguments that her government's primary responsibility should be to maintain the country's prosperity.

The officials also know that countries such as Australia, India and Singapore are unlikely to engage in serious free trade negotiations with Britain until its own trade relationship with the EU becomes clear. So the current attention lavished in London on free trade discussions with countries outside the EU are just political manoeuvres, designed to appease anti-EU hardliners rather than serious efforts to conclude new trade deals.

But faced with these tensions in her party, officials close to the Prime Minister now accept that she will be unable to prevaricate much further than the first week in October, when her ruling party holds its annual conference.

For that would be the moment when Mrs May would be expected to explain to delegates what her "Brexit means Brexit" slogan actually means.