Brexit secretary Dominic Raab is set to warn that the EU could force Britain into a no-deal Brexit.

He will say that Britain should pursue a no-deal Brexit sooner than remain in the EEA or a customs union with the EU.

"If an attempt is made to lock us in via the back door of the European Economic Area (EEA) and customs union ... then we will be left with no choice but to leave without a deal," he is expected to say.

Raab's speech comes at the early stages of the Conservative party conference in Birmingham which is straining already tense relations within Cabinet to breaking point.

LONDON — The UK would crash out of the EU without a deal rather than pursuing a soft Brexit, Dominic Raab will warn today.

Speaking at the Conservative conference in Birmingham, the Brexit secretary will warn the UK will be "left with no choice" but to pursue a no-deal Brexit if the EU fails to offer a favourable agreement.

"Our willingness to compromise is not without limits," Raab is expected to say.

"We are leaving the European Union in fact, not just in name. If we can't obtain a deal that secures that objective ... if an attempt is made to lock us in via the back door of the European Economic Area (EEA) and customs union ... or if the only offer from the EU threatens the integrity of the Union, then we will be left with no choice but to leave without a deal."

Theresa May has repeatedly ruled out remaining in the EEA because it would force the UK to retain the EU's freedom of movement policy, while a customs union would limit the UK's ability to strike independent trade deals.

Raab will insist that his approach to negotiations is "pragmatic, not dogmatic" and say the UK's proposed divorce deal "manages the risks of Brexit." Notably, however, his speech does not appear to name-check the "Chequers" deal which refers to Theresa May's divisive Brexit blueprint.

Several Cabinet ministers have stopped using the word because it is so unpopular among party members.

Raab's speech comes at the early stages of a party conference in Birmingham which is straining already tense relations within Cabinet to breaking point.

In an interview on Sunday, Boris Johnson launched a broadside at the prime minister, describing her plan for leaving the EU as "deranged."

May subsequently gave a standing ovation in Birmingham at a speech where Digby Jones, the former director-general of the CBI, described Boris Johnson an "an irrelevance" and an "offensive person."

Raab, who campaigned to leave the EU, was appointed as Brexit secretary in July following the resignation of David Davis.