Former House of Commons Speaker John Bercow has given a withering assessment of Theresa May's deal with the DUP to prop up her Government in his newly published memoirs.
The former Conservative MP said that the Tories' confidence and supply arrangement left the former Prime Minister "politically boxed in" because she was "in hock to the DUP".
In his new book he also said that in his opinion, like Scotland, Northern Ireland's place within the Union "is more fragile and precarious than ever".
Mr Bercow (57) spent 12 years as Speaker before stepping down last year - and just as he courted controversy in his parliamentary role, so he has done so by pulling no punches in print. He described Mrs May as "stubborn when flexibility was needed and, lacking a natural majority and in hock to the DUP, she appeared frozen, politically boxed in, almost paralysed and unable to chart a clear and safe course for the UK".
"In a contest as to who has been the worst Prime Minister since 1945, it is hard to choose between Anthony Eden and Theresa May," he wrote.
In his newly published autobiography, Unspeakable, Mr Bercow said he feared that the Brexit deal under Boris Johnson could "trigger the break-up of the Union".
"For better or for worse, Scotland's place in the Union is more fragile and precarious than ever. The same could be said for Northern Ireland.
"The pro-Brexit Democratic Unionist Party lost two of its 10 seats, including that of its Westminster leader, Nigel Dodds. Sinn Féin took seven, the SDLP won two and the Alliance Party secured one.
"The DUP now represents a minority of Northern Ireland's Westminster seats after enduring an unprecedently bad election. It is also a matter of record that Northern Ireland voted in the 2016 EU referendum to remain, and the fact that the DUP backed Brexit against the majority wish of the province's electorate damaged its standing with voters.
"Under the terms of the Johnson Brexit deal, goods from Northern Ireland as well as the Republic of Ireland will face new paper checks and this may prove deeply unpopular.
"Any goods going from Britain into Northern Ireland will be subject to an EU Customs Code, effectively an Irish Sea trade border.
"The Unionists remain firmly opposed to the Johnson Brexit deal but have no leverage at Westminster. Nationalists of every hue are against Brexit in any form.
"The Unionists want above all to remain in the UK. By contrast, nationalists who are growing in numbers would prefer a united Ireland and the prospect of it is undoubtedly greater than before the Brexit imbroglio began.
"The irony of all of the above is that an avowedly unionist party - the Conservatives - has won its biggest majority for three decades in circumstances which could trigger the break-up of the union of the United Kingdom of Great Britain and Northern Ireland. Sure enough, truth can be stranger than fiction."