Theresa May has been likened by Sir Vince Cable to a hostage “handcuffed to a radiator in the basement of a flat in Beirut” as the Lib Dem leader criticised the Prime Minister’s handling of Brexit.

Sir Vince said Mrs May was at the mercy of Eurosceptic Tory MPs and that if she does not listen to their concerns over the UK’s withdrawal from the European Union “she’ll be out”.

He also claimed that Brexit might not happen because the Government is so “horribly unprepared” for negotiations with Brussels.

Sir Vince told Buzzfeed that the Prime Minister was in a “very awkward position” on Brexit.

Theresa May, the Prime Minister credit: Chris J Ratcliffe /AFP

He said: “It’s a bit like being handcuffed to a radiator in the basement of a flat in Beirut and she is at the mercy of other people.

"The minute she shows a sign of independence of mind there will be 70 letters that will go into the chairman of the '22 committee [the Tories' influential backbench group of MPs] and she’ll be out."

Downing Street would not be drawn on whether the Prime Minister thought Sir Vince’s comments were helpful.

A spokesman said: “Our focus is on securing a good deal for the UK and the EU and we are making concrete process in the negotiations.”

Sir Vince has previously set out his belief that the UK’s divorce with Brussels might not go ahead.

He has conceded that such an outcome is unlikely but he remains convinced that Britain could remain in the bloc.

He said: "I wouldn’t say it’s probable, but it’s certainly possible that it may never happen.

"Because the process is so unbelievably complicated and the government clearly is horribly unprepared for these negotiations."

Sir Vince became leader of the Lib Dems after Tim Farron quit the role in the wake of a general election in which the party’s anti-Brexit message failed to translate into major electoral success.

The new leader believes the way in which the party offered voters a second referendum on the terms of the Brexit deal was a mistake in comments which are likely to be interpreted as thinly veiled criticism of his predecessor.

He said: "I think to be frank it didn’t play well in the general election – I think people didn’t understand what we were trying to say.

“This was our fault, of course. It came across to people as rerunning the last one, which is not what it’s about.”

Sir Vince said the second vote should be seen as a “first referendum on the facts”.

His comments come ahead of the Lib Dem autumn conference which is taking place in Bournemouth and starts on Saturday.