BORIS Johnson has vowed to take the UK out of the EU “deal or no deal” at the end of October if he becomes prime minister.

The frontrunner to succeed Theresa May said the only way to secure a solid agreement with Brussels was to “prepare for no-deal”.

The comments could spark alarm among Tory MPs who have voiced concern at ushering in a new prime minister who might take the country out of the bloc without an agreement in place with the EU.

Business leaders have also spoken out about the need to avoid a no-deal exit and the damage it could do to the British economy.

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Johnson’s remarks came just hours after May announced she would quit as Tory leader on June 7, with a successor set to take over in Downing Street towards the end of July.

Speaking at an economics conference in Switzerland, the former foreign secretary echoed May’s mantra that “no deal is better than a bad deal” when he said: “A new leader will have the opportunity to do things differently and have the momentum of a new administration.

“We will leave the EU on October 31, deal or no deal. The way to get a good deal is to prepare for a no deal.”

Earlier this week more than 30 Tory MPs said they would fight against any leadership candidate who is prepared to take the UK out of the EU with no deal. However, if the UK does not agree its terms of departure and does not seek or is granted a further Brexit extension, it would crash out with no deal “by accident” at the end of October.

European figures issued a warning that the Brexit deal they negotiated with May still stood.

A spokeswoman for European Commission president Jean-Claude Juncker said: “The president very much liked and appreciated working with Prime Minister May, and has said before, Theresa May is a woman of courage for whom he has great respect. He will equally respect and establish working relations with any new prime minister, whomever they may be, without stopping his conversations with Prime Minister May.”

But she stressed: “We have set out our position on the withdrawal agreement and on the political declaration.

“The European Commission and the Article 50 format has set out its position and we remain available for anyone who will be the new prime minister.”

Manfred Weber, an ally of German chancellor Angela Merkel and the

centre-right’s lead candidate to replace Juncker after the European elections, said Brexit was a “total disaster” but May “fought for a stable solution and a viable deal”.

But he continued: “We hope once more for a constructive approach from our British partners. I appeal to the UK’s sense of responsibility and leadership in these times of great uncertainty.”

Dutch PM Mark Rutte stressed the Withdrawal Agreement “remains on the table”.