You could have a POD of 1970 following the discovery of North Sea Oil.
The Scots demand to see some of the money spent on them, Edward Heath and the British government tell them to get stuffed, (diplomatically of course).
This leads to a rise to promenance of the Scottish Nationalist Party, and occupying joint second place with Labour, the Scottish Socialist Party. In 1979, the Conservative party do not field any candidates in Scotland, knowing that they will not be elected.
Keep the rest of history as it is until 1997.
1997, despite being the least popular government in modern history, the Conservative party under John Major win the general election. Rumours of gerrymandering, missing vites and later, outright fraud cause a massive outcry from the press. Even the Sun, normally a vocal supporter of the Conservative party passes concerns that things may not have been as they should have been.
The SNP comissions a poll across Scotland asking "Should Scotland become independant of Westminster?"
The result comes back with an unprecedented 68% YES vote. The SNP begin a campaign demanding a Referendum on Scottish independance. Westminster again refuses.
In 1998, following a leaked report from the Independant Electoral comission alledging widespread vote fraud, the LSE suffers a 18% crash in value. Britian plunges into economic meltdown.
Alex Salmond again demands a referendum, this time when denied, following a back room deal with the other Scots parties, (including the nominally unionist Labour and Liberal Democrat parties), Alex Salmond makes the Holyrood speah setting out a unilateral declaration of Scots independance under the Crown. At the heart of it, a simple line, "and with this step, we will not only forge a new future for Scotland with the fruits of our labours, but with the fruits that Scotland has been blessed with, so long plundered by our former masters in Westminster".
And thus, the first Salvo of the Scottish Oil Wars, (as opposed to the 3 day "Fish War" of 1999), was fired.
Following the unsuccessful attempt to bring Scotland back into the fold, Yorkshire, (Yorkshire, North Yorkshire, South Yorkshire and West Yorkshire combined), declare their independance with the assistance of the catterick Garrison. Northumberland and Lancashire petition to join and the York & Northern Commonwealth comes into existance. Northumberland and Durham, cut off from the rest of England become defacto but independant member of Y&NC shortly afterwards. Again. although they have declared themselves independant of Westminster, they have declared themselves Independant under the Crown, retaining King Charles II as their King as had Scotland before them.
My first attempt at a Map
By the way, Cornwall also declared independance, but seeing as they don't interfere with the Royal Navy bases there and also accept the cron, no one is too fussed.