Disgruntled Conservative MPs are threatening to vote against fulfilling the 'vow' for Scottish independence - while the Liberal Democrats are threatening to block a vote on the pledge in the first place.
Right now the turmoil over whether and how to keep the promises made by Westminster's three party leaders to the people of Scotland is being kept firmly behind closed doors.
But frustrations on both sides of the coalition and a deepening split with the Labour party this autumn are steadily reducing the chances of agreement being reached along the lines of the timetable set out before the September 18th 'No' vote.
It might sound like bad news for the Conservatives, but this is actually a win-win scenario for them. Whatever the outcome, it's likely to make Ed Miliband's chances of getting into No 10 as prime minister all the slimmer.
Tory rebels ready to defy Cameron
Emerging evidence of the concerns of suspicious Tory backbenchers - those who are simply not prepared to back Cameron's promise without a comparable deal for England - will be alarming news for the government.
One Conservative MP said: "The deal was done by Gordon Brown without any consultation. In principle I have no problem whatsoever with more devolution for the Scots, but that has to go in tandem with English votes for English laws. The deal has to be done together, not one then the other. What is sauce for the goose has got to be sauce for the gander."
'In tandem' is an unfortunate phrase. It was first uttered by the prime minister on the morning of September 19th and implied that Scottish devolution could not take place without devolution for the rest of the UK.
That is exactly what Cameron meant. But it was an awkward choice of words, and in the following days the Conservatives realised a standoff over the English question risked the pledge to Scottish voters sliding. Unfortunately that is exactly what now looks like happening.
Senior Tories also realised there was great potential to politicise the issue. So, by U-turning, Downing Street isolated Miliband as the only party leader opposing English votes for English laws.
That has allowed Labour to be painted as the party letting down 85% of the population. Never mind that the opposition has unveiled an impressive-looking package of devolution. "English votes for English laws is not about devolution," as one source close to the Labour leader put it. "It's about the mechanics of this place for the political advantage of the Conservative party, even if it breaks up the United Kingdom."
Labour has steered clear of the cross-party talks being held on English devolution in a sub-committee of the Cabinet chaired by William Hague. That means the leader of the House's proposal to hold a Commons vote on the issue if a deal is not reached by the end of November is very much a live one.
The division, if it actually happens, is set for either side of Christmas. And the Tories are upbeat. If it came to it, Conservative strategists remain optimistic they could win a Commons vote even in the face of united opposition from Labour and the Lib Dems.
Persuading a handful of frustrated Labour backbenchers to rebel is always going to be difficult, however, and the suspicion of the Tories' partisan motives that unites Labour and the Lib Dems will probably be strong enough to block them.
Now the negative noises being sounded by some Tory MPs is making such a Conservative victory even more unlikely.
One former minister said the idea an English deal could be reached in keeping with the Scottish timetable was "ridiculous" and that he intended to rebel over the vow as a result.
"I will be voting against further devolution for Scotland as promised by Gordon Brown and signed up to by the leader of my party," he told Politics.co.uk.
"He [Cameron] had no mandate so I don't feel bound to support that idea. I wasn't elected on that proposition."
When asked whether he thought other Tory MPs would join him, the ex-minister added: "I'd be very surprised if there weren't. There was considerable disquiet at the prime minister's decision to get Gordon Brown to announce a new policy when it's specifically not been negotiated out of the options available to the Scottish people in their referendum. The PM felt it was necessary to save the union. That was his judgement, not mine - but then again, I'd probably put rather less store by the union than he does."
The message of these MPs to William Hague is simple. Don't expect their support for devo-max until it's clear it represents a fair financial deal to constituents in England - and that the English votes for English laws question has been settled for good.
A Lib Dem spanner in the works
There is a further problem faced by Hague and Cameron: the risk that agreement with the Lib Dems could prove equally elusive.
The initial deadlock was over the makeup of a grand committee of English-only MPs put forward by the Lib Dems.
The coalition's junior party has been arguing that proportional representation is how the elected assemblies of the devolved institutions are chosen; the Tories respond by saying they refuse to accept any reduction in their influence in the Commons.
Despite the initial deadlock a deal might still be possible. As Politics.co.uk reported earlier this week, the Lib Dems could be prepared to give way if the Conservatives accept a big idea known as 'democracy on demand'.
The stakes are high for the Tories. If they accept the Lib Dem proposals power could leak out of Whitehall like a sieve. If they refuse, it's now emerged, the Lib Dems are threatening to block Hague's cherished vote on the issue.
A motion of the kind Hague wants would have to be put forward by the government. It would be impossible if the Lib Dems, frustrated by the talks, chose not to play ball. As one source put it: "Why would we agree to a motion when there's no cross-party agreement?"
An impasse with the Liberals would force the Tories to resort to asking helpful Conservative MPs to seek a vote in the sliver of Commons time controlled by backbenchers.
Such a move would only make already-strained coalition relations frostier after the parties blocked each others' bids to legislate for an EU referendum and dilute the impact of the bedroom tax last month.
Bad news for Ed
Of course the party leaders need time to secure consensus. Their problem is they have very little of it.
In Westminster the coalition's secret talks, backbench mutterings and Labour suspicions are set to continue all the way up to the vote which may, or may not, actually happen.
Right now none of the three main parties are in agreement. This opens up the possibility that nationalists will be given free rein to protest the timetable for the Scottish vow is not being upheld.
Such an outcome would not be so bad for the Tories.
Anger with the Westminster parties would only serve to help the cause of SNP candidates taking on Labour north of the border.
The nationalists can point to Brown's promise of a second reading bill before the general election as proof that the English can't deliver what they promised.
Gordon Brown is expected to be one of the four Scottish Labour MPs who retains his seat. (via MORI poll) pic.twitter.com/hOXfbXRphv— Britain Elects (@britainelects) October 30, 2014
The Conservatives will argue that was never part of the deal and insist they only need to produce a draft bill before May next year.
It's an approach that won't put off Tory voters in their English constituencies, but will strengthen the hand of the nationalists in Scotland.
The SNP is looking to make substantial gains in 2015. These will come at the expense of Labour, further diminishing Miliband's chances of ending up in Downing Street.