The accusation came as MPs prepared to vote on an amendment tabled by former attorney general Dominic Grieve which would effectively block Tory leadership frontrunner Boris Johnson from suspending parliament to force a no-deal Brexit through.
The insider said that No 10 could have stopped the vote - along with a failed cross-party attempt last month to seize control of the parliamentary agenda in order to prevent the UK leaving the EU without a withdrawal agreement on 31 October – if its focus was fully on giving Theresa May’s successor the best chance of delivering Brexit.
Mr Grieve’s amendment to Northern Ireland legislation would require the prime minister to report back to MPs every fortnight on progress in restoring power-sharing government at Stormont.
This would effectively force the Commons to be sitting in the run-up to the Halloween deadline for Brexit, preventing the PM from using a procedure known as prorogation to lock MPs out of parliament.
Speaking to The Independent on condition of anonymity, the government insider said there was frustration in Conservative ranks that Downing Street was allowing opponents of Brexit opportunities to tie the future prime minister’s hands.
There was a feeling that Number 10 was concentrating on delivering plans to provide Theresa May with a positive legacy, rather than keeping its eye on the Brexit ball, said the insider.
By allowing opponents of EU withdrawal opportunities to seize the initiative, they risked denying Mr Johnson – or his leadership rival Jeremy Hunt – use of vital weapons which would convince Brussels that the UK was serious about the option of no-deal and force the EU to make concessions.
“If they were expecting to stay in government, they would not be allowing these elephant traps to be laid,” said the insider.
“There’s bitterness. I’m not saying Theresa May but people around her.”
The source said that Number 10 could have stopped both Mr Grieve’s amendment and June’s opposition day motion from ever coming before the Commons – and would probably have done so if the current team expected to stay on to negotiate Brexit.
Jeremy Corbyn’s failed attempt to seize control of the Commons agenda – backed by Tory grandee Sir Oliver Letwin – could have been avoided by simply not providing Labour with an opposition day when it chooses the motion for debate.
And the problem of extending beyond the end of August the deadline for elections to the devolved assembly in Northern Ireland could have been overcome without recourse to legislation in the Commons which would inevitably be vulnerable to amendment by anti-Brexit rebels.
If selected for debate by the speaker, John Bercow, the Grieve amendment could provide the breakthrough Remainers have been looking for to dash Mr Johnson’s plan for withdrawal on 31 October, deal or no deal.
So great are the stakes that former minister Justine Greening has issued a challenge to cabinet opponents of no deal like Philip Hammond and David Gauke to back Mr Grieve’s amendment even if it means losing their jobs.
“Downing Street could have stopped this. That is what most people think,” said the insider. They could have pulled the bill.
“It could have been put off into the summer. There are other ways to get around this.”
Government sources rejected the claims, arguing that today’s Northern Ireland (Executive Formation) Bill is essential for administration to continue in the province in the absence of a power-sharing executive, and that Labour was entitled to more opposition days as it was an extended parliamentary session.
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