Theresa May has vowed she will “deliver” a new trade deal with the EU before Brexit, toughening up her commitment for the exit talks.

Speaking at prime minister’s questions, the Prime Minister told MPs she would prevent Britain crashing out of the EU – at potential huge economic cost, say critics.

In her landmark speech yesterday, Ms May said only that she was “confident” that a fresh agreement can be struck, despite the tight 18-month timetable.

And she threatened to walk away with “no deal” if necessary – which would inflict punishing World Trade Organisation tariffs on businesses.

But, at prime minister’s questions, Ms May insisted that would not be necessary, as she clashed with Jeremy Corbyn over her Brexit strategy.

She said: “The whole point is that we will negotiate a free trade agreement with the European Union that is about the best possible access for British business to operate in the European Union member states and for European business to operate here in the United Kingdom.

“It’s about sitting down and negotiating the best possible deal for the United Kingdom.

“That’s what I’m committed to – and that’s what this Government is going to deliver.”

The high-profile promise – made on the floor of the House of Commons – raises the stakes for the negotiations to come, after the Article 50 exit clause is triggered.

Speaking 24 hours earlier, the Prime Minister had said: “I am confident that a deal - and a new strategic partnership between the UK and the EU – can be achieved.”

And, making clear how willingness to walk away if necessary, she added: “I am equally clear that no deal for Britain is better than a bad deal for Britain.”

The idea of a trade agreement within 18 months – to allow the EU to ratify it, before the two-year Article 50 process is completed – is widely seen as unrealistic.

Later, in answer to a Conservative backbencher who argued leaving the EU with no deal must not become the “preferred option”, she replied: “Absolutely.”

During the clashes, the Labour leader accused Ms May of “demeaning” Britain by threatening to make the UK an offshore tax haven, if she cannot get the Brexit deal she wants.

Mr Corbyn called on her to “stop her threat of a bargain basement Britain, a low-pay tax haven on the shores of Europe”.

And he said: “It wouldn't necessarily damage the EU, but it would certainly damage this country - businesses, jobs and public services.

“She demeans herself and her office and our country's standing by making these kinds of threats.”

Mr Corbyn also accused the Prime Minister of failing to guarantee the future of thousands of EU nationals working in UK public services - or to explain whether she would be willing to pay for continued access to the single market.