Scotland's rejection of independence has saved David Cameron from going down in history as the Prime Minister who presided over the break-up of the United Kingdom, and has seen off any immediate threat to his position.

But wrangling over the UK's constitutional settlement now looks set to overshadow the remainder of his term in 10 Downing Street after concessions he offered on devolution angered MPs south of the border.

In a live televised address from No 10 following the declaration of the final result, Mr Cameron not only spelled out plans for greater home rule for Scotland, but also offered a significant rebalancing of the way the four nations of the UK are represented.

Already disgruntled by what some of them viewed as Mr Cameron's lacklustre handling of the referendum campaign, a number of Conservative MPs were dismayed by his decision to join Deputy Prime Minister Nick Clegg and Labour's Ed Miliband in a last-minute promise of "extensive new powers" for Scotland in the event of a No vote.

The promise means the Prime Minister will immediately be thrust into tortuous negotiations over the future of tax, spending and welfare in a Scotland operating under "devo-max".

And it also forces him to confront the grave misgivings of English MPs who fear that their regions will be overlooked in the rush to placate the Scots.

Crucially, the pledge - hastily drawn up in response to a shock opinion poll suggesting that momentum was with the Yes campaign - included a promise to maintain the "Barnett formula" for allocating resources to the nations of the United Kingdom.

The formula has long been a bone of contention among Tories from south of the border, angry that it guarantees more spending per head to Scotland than England.

Transport minister Claire Perry has warned against showering Scotland with "financial party bags", which she said "can hardly be equitable" for English voters, while another unnamed Conservative predicted a "bloodbath" if Barnett - in place since the 1970s and disowned even by its own creator - is not reformed.

Mr Cameron will have to be prepared to rein in potential rebellions from Conservatives opposed to any further leaching away of authority from Westminster to rival centres of power.

And he will also face calls for devolution of more powers not only to Edinburgh, but to Wales, Northern Ireland and the regions of England. Tory MP Christopher Chope has already warned that he is ready to vote against a "devo max" package unless there is a wider examination of the balance of powers within the UK as a whole.

A sizeable tranche of Tory MPs is certain to demand that any handover of power to Holyrood is balanced by restrictions on the ability of Scottish MPs to vote on English matters in Westminster, while senior backbencher Bernard Jenkin has suggested that Scots may have to be excluded from key ministerial posts, including chancellor of the Exchequer. Meanwhile Brigg and Goole MP Andrew Percy issued a call for an English parliament.

As he prepares for a general election in less than nine months, Mr Cameron will not relish the prospect of running skirmishes with his own side over devolution.

Meanwhile, the spectacle of their leader handing over powers from Westminster to the Scottish Parliament is unlikely to inspire Eurosceptic backbenchers with confidence in his ability to claw back powers from Brussels in the renegotiation of Britain's EU membership he has promised after the election.

Some Tories blame Mr Cameron personally for allowing the independence vote to go ahead, and for doing so on terms which they believe gave SNP leader Alex Salmond a strong hand to play.

And his image as a "winner" has not been enhanced by the fraught final days of campaigning, when he was accused of panicking as it briefly appeared that the No camp had let a 20-point lead slip away.

Ironically, Conservatives had most to gain electorally from Scottish independence. While independence would have inflicted savage reductions on Labour and Liberal Democrat representation at Westminster, the Conservatives have only one Scottish MP to lose.

But few Tories will see it as a missed opportunity. Despite having little or no representation in Scotland since 1997, most Conservatives regard the preservation of the Union as a fundamental part of their core beliefs. Few would trade the unity of the UK for the prospect of permanent rule in the rump which would remain if Scotland left.