A Tory MP is threatening to wipe out Boris Johnson's majority altogether by defecting to the Liberal Democrats.

Dr Phillip Lee, who supports a second EU referendum, suggested he will 'spend the summer' deciding whether to cross the floor.

Mr Johnson suffered a hammer blow last night when the Conservatives lost the Brecon & Radnorshire by-election, slashing his effective majority to just one.

But Dr Lee switching sides would reverse the numbers - meaning that Opposition parties have one more MP than the government. .

Speaking on a podcast with fellow Tory Remainer Sam Gyimah, Dr Lee was asked whether he could defect to the Lib Dems under new leader Jo Swinson.

'The party I joined was the party of John Major and John Major, I think, is probably feeling like this judging by his contributions in recent weeks,' he said.

'I'm really not comfortable about my party pushing for no-deal Brexit without proper consent of the public.

'Purely on the national interest, I think it's wrong to do this. But party politically I think it's narrowing our base in a way that I don't see how we win elections.

Dr Phillip Lee, who supports a second EU referendum, suggested he will 'spend the summer' deciding whether to cross the floor

'And if you don't win elections in a democracy you don't have power and you can't do things you want to do. It's just simple reality.

'I'm sort of sitting here, looking on and - yeah - I'm going to spend the summer thinking a lot.'

Three Tory MPs - Anna Soubry, Sarah Wollaston and Heidi Allen - quit earlier this year to join an independent grouping in the House of Commons.

There are currently 320 MPs who - on paper - would back the Government in a crunch vote in the House of Commons - 310 Tories and 10 members of the DUP.

The DUP agreed to support the Conservatives in certain key votes, such as confidence motions and Budgets, as part of a deal reached in the aftermath of the 2017 general election.

After the by-election, there are 319 MPs from all other parties set against the government total of 320.

These totals do not include Sinn Fein's seven MPs, who do not take their seats in the Commons, and the Speaker and three Deputy Speakers, who do not vote.

Jane Dodds (centre) won the Brecon by-election for the Lib Dems with a majority of 1,425, and said the result was 'sending a message to Westminster that we demand better'