PRO-EU MPs have expressed alarm that Britain could leave the European Union without any transition period if there is no deal on a new free trade agreement.

Their fears were raised when Theresa May said in order to have a transition to a new partnership arrangement with the EU following Brexit, the terms of that arrangement would have to be clear beforehand.

Following last week's EU summit in Brussels, the Prime Minister in a Commons statement said she remained "confident" she would be able to get that "new, deep and special partnership" with the EU.

However, Labour MPs said if she failed to get an agreement and there was no transition, businesses would face the "cliff-edge" break which they had long feared when Britain leaves in March 2019.

Mrs May told the Commons: "The point of the implementation period is to put in place the practical changes necessary to move to the future partnership; in order to have that you need to know what the future partnership is going to be."

The PM was pressed by Labour’s Yvette Cooper, who warned that Britain could be forced to fall back on World Trade Organisation rules.

"If we haven't got a long-term trade deal agreed by this time next year, then there won't be any transition deal at all and Britain will end up on WTO rules by March 2019," declared the former Shadow Home Secretary.

Her colleague Chris Leslie also urged Mrs May to commit to negotiating a transitional arrangement separate from a trade deal.

"It is the cliff edge that the business community want to know will not be there in 2019," he said.

Mr Leslie later tweeted that her refusal to offer the reassurance he asked for would be a "disaster" for business planning.

The Liberal Democrats also claimed the PM appeared to rule out a Brexit transition period unless a final deal had been approved.

"This defeats the whole point of a transition deal, which is to provide much-needed certainty," declared Sir Vince Cable.

"Past experience shows there is no way a final trade deal with the EU will be agreed by March 2019. Firms facing crucial investment decisions need clarity now, not in another 18 months' time," added the party leader.

Ian Blackford for the SNP urged the PM to push to secure a transitional arrangement after she again refused to rule out a no-deal Brexit scenario.

"The Prime Minister is being held to ransom by her chaotic Cabinet,” insisted the Highland MP.

“Today’s statement was another opportunity for Theresa May to unequivocally rule out a nightmare no-deal exit from the EU. Yet, once again, she failed to offer the certainty that the UK’s economy, businesses and jobs market so desperately need.”

Anna Soubry, the former Business minister and prominent Remainer, made reference to a letter, signed by five of the UK’s biggest business lobby groups, which she said warned of the "consequences of no deal and relying on WTO rules".

"Will the Prime Minister agree to listen to British businesses and would she even go so far today as finally to rule out no deal," asked the Nottinghamshire MP.

But Mrs May noted: “The best way to get a bad deal for the UK is to say that we will accept anything that they give us, regardless.

"We have to be clear that what we are working for is a good deal but I am optimistic about that because we have made some progress and the good deal that we're seeking is in the interest of both sides," she added.

Europhile Ken Clarke, the former Chancellor, said the "main problem is other European leaders can see a noisy minority in the Cabinet and on the backbenches of her own party have persuaded themselves that no deal at all is completely desirable".

But his Conservative colleague John Baron noted: "The Prime Minister is absolutely right not to rule out a no deal scenario; to do otherwise would be utterly naive."