Update | Referendum start of change for UK, say Scotland's 'Yes' and 'No' camps

Scotland's "No" to independence may have saved British Prime Minister David Cameron his job, but sweeping pledges of a constitutional shake-up could undermine his re-election drive and trigger more political instability.

Responding to what he called a "clear" rejection of Scottish independence yesterday, Cameron, who is up for re-election in May, promised to begin a process that would see Scotland granted further powers.

He also said he wanted to see more powers devolved to Wales and Northern Ireland, as well as changes for England, starting with new voting arrangements in the British parliament.

Some, including in his own party, feel he promised too much.

"This result presents both opportunities and challenges for Cameron," said Matthew Ashton, a politics lecturer at Nottingham Trent University. "On the one hand he can make claim to the title of 'the man who saved the union'. On the other, he'll now have to deliver on his extraordinary ambitious promises of a new constitutional settlement."