The prime minister thought he had his paperwork complete after months of delicate negotiation.

All he needed was clearance from the Democratic Unionist Party (DUP) and his backbench Brexiteer MPs before signing off with the EU.

But, as his predecessors at Number 10 discovered, dealing with the DUP is challenging.

Thanks to those same predecessors, trust between DUP leader Sir Jeffrey Donaldson and the Tory leadership has been slowly eroded.

That is why the party was not moved by the assurances offered by the prime minister in the House of Commons on Wednesday.

"We've heard the same warm words from the same dispatch box before, it counts for nothing," said one DUP MP.

That is why the DUP leader warned against "tweaking" the protocol and demanded the "legally binding text" be rewritten.

Unless the DUP can read it in a bill, they can't sell it.

While sidestepping that part of Sir Jeffrey's question, the prime minister hinted in another answer that legislative changes are in the mix.

That will be key for the DUP to be able say the old Northern Ireland Protocol is gone.

But any changes will come in the form of new legislation "overlaying" what has gone before both in London and Brussels.

Overlay but not replace.

So the EU will equally be able to say the original protocol text remains.

Nuances like that matter when it comes spinning and disguising compromises if we ever reach the point of a deal.

Judging by the Westminster whispers this week that is far from clear.

There is real concern among some less vocal Tories that a deal which was within touching distance could slip through their grasp.

Some of those non-European Research Group (ERG) MPs question why the Prime Minister is spending so much political capital on an issue which does not stir their voters at a time when other more pressing issues need attention.

The protocol does not appear in Mr Sunak's five key priorities and there is a budget looming within weeks.

"There are some on our back benches who are certifiable and Mr Sunak needs to stand up to them" said one frustrated Tory.

After briefing heavily that the deal was to be published this week, Team Sunak are now in crisis management.

The daily calls with European Commission Vice-President Maros Sefcovic on the surface suggest Brussels is being squeezed for more concessions, but equally it could be for the optics ahead of a deal being agreed next week.

Real progress?

Mr Sunak has invested too much to walk away.

He cannot sit on a deal which provides much needed remedies for businesses struggling under the burden of the Northern Ireland Protocol.

Plus, he is desperate to bank the gains he has secured.

That may include taking back control of state aid, VAT and other tax breaks in Northern Ireland which, under the protocol, fell to Brussels.

That was leaked this week and was not totally discounted by sources in Brussels.

Such leaks are useful in countering back bench and DUP pressure in the absence of publishing the deal.

Could this be one of the important areas where Sir Jeffrey Donaldson told us real progress has been made?

But what the prime minister really needs is for the DUP to hold back on its verdict of any deal.

This would allow the government time to win over business leaders and other stake holders before the DUP passes judgement.

But if the government is to secure its goal of restoring the Stormont institutions then the DUP will have to be won over at some stage

The party is expecting the deal to be published early next week and it will likely flag concerns but reserve full judgement until it sees any accompanying legal text

With a council election looming in May, rejecting the deal is the easiest option for Sir Jeffrey.

But saying no is not a long term sustainable position and that is the calculation the government will be banking on .