Ed Miliband and his UK Labour Party will breathe a huge sigh of relief at the Scottish people's rejection of independence.

Not only would a Yes result have been potentially politically terminal for the leader, but it would have threatened the very nature of a party that draws heavily on its strength north of the border.

But the No vote is far from the end of Mr Miliband's problems.

The frantic efforts to secure the union saw pledges of more autonomy for Scotland.

And that has already triggered a renewed drive for English devolution that could prove almost as damaging to Labour's prospects.

The so-called "West Lothian question" - which asks why Scottish MPs at Westminster should be able to vote on matters that do not affect their constituents - has been rankling for many years.

Although politicians from all sides have recognised there is a real issue, the general consensus has been that - as Labour's ex-lord chancellor Lord Irvine once pithily remarked - the best answer to the West Lothian question is to stop asking it.

A commission led by Sir William McKay, a former clerk of the House of Commons, stopped short last year of recommending fundamental change, instead suggesting a handful of procedural tweaks, such as formally noting whether there was an English majority in favour of laws that only cover England.

But the delicate truce may not survive another significant transfer of powers to the Scottish Parliament.

Some Tory MPs have already been muttering darkly about blocking a new "devo-max" package. Others are demanding an English-only parliament to restore what they see as a democratic deficit - although David Cameron has insisted that is not "remotely" close to happening.

Liberal Democrat leader Nick Clegg has said it would be "unfair" to leave Westminster out of the impending "rewiring" of the UK constitution.

Labour's reliance on its usual quota of 40 or so Scottish MPs to form governments can be overstated.

Only four general election contests since 1945 would have had a different result without Scotland, and Tony Blair would still have enjoyed comfortable majorities in 1997, 2001 and 2005.

But polls are suggesting that Mr Miliband is currently on track for a slender majority next May - leaving him deeply vulnerable to such reforms.

For example, if Scottish MPs were barred from voting on issues that had been devolved north of the border, a Labour government could suddenly find itself unable to get key elements of a Budget package through the Commons.

The No vote may have killed off Scottish independence for now, but it seems the constitutional upheaval in the UK could be just beginning.