Tory leadership rivals Boris Johnson and Dominic Raab were last night blamed by Theresa May’s allies for dashing her hopes of a Brexit deal with the DUP.

They claimed a last-minute accord fell through because of doubts among the Northern Irish party that Mr Johnson and Mr Raab were ‘really Unionists’.

A senior Cabinet Minister told The Mail on Sunday that the two men had met the DUP as the Prime Minister desperately tried to persuade the party’s ten MPs to add their crucial support to her deal.

May's allies claimed a last-minute accord fell through because of doubts among the Northern Irish party that Mr Johnson (pictured) and Mr Raab were ‘really Unionists’

A senior Cabinet Minister told The Mail on Sunday that the two men (Raab is pictured) had met the DUP as the Prime Minister desperately tried to persuade the party’s ten MPs to add their crucial support to her deal

But the Minister – a close ally of Mrs May – said the DUP had suspicions about how strongly former Foreign Secretary Mr Johnson and ex-Brexit Secretary Mr Raab really felt about the Union.

The May ally suggested that the DUP had doubts over how strongly either man would defend the Northern Ireland position if they became Prime Minister.

He said: ‘One of the things that put the DUP off is that they met Boris Johnson and Dominic Raab and decided that they were not really Unionists.’

The backing of the DUP is seen as vital to any hopes Mrs May has of getting her Brexit plan over the line.

But the party has held firm against it, with its Westminster leader Nigel Dodds saying: ‘I would stay in the EU rather than risk Northern Ireland’s position.

‘That’s how strongly I feel about the Union.’

The May ally suggested that the DUP had doubts over how strongly either man (Johnson pictured with May in 2017) would defend the Northern Ireland position if they became Prime Minister

Mr Dodds has consistently raised fears of Northern Ireland being reduced to a separate status from the rest of the UK because of the Brexit backstop agreed between Mrs May and Brussels.

However, there were also reports that privately the DUP had been split 7-3 in favour of backing the Prime Minister’s deal but in the end maintained a united front to oppose it.

Last night, friends of Mr Johnson dismissed the claims that he had ‘put off’ the DUP.

They pointed out that he had been feted by the party when he attended their annual conference in Belfast, when he railed against the danger of having to ‘leave Northern Ireland behind as an economic semi-colony of the EU’ and of ‘damaging the fabric of the union’.

Allies of Mr Raab also dismissed the claims.