Britain Divided....
A couple of interesting scenarios - the first is arguably much more realistic. The POD is that both Scotland and Wales vote in favour of devolution in the 1979 referenda (in OTL neither proposition got enough support to be carried).
In May 1979, the Conservatives under Margaret Thatcher win the General Election but in Scotland the Assembly elections deliver a Labour majority with the SNP close behind the Tories. In Wales, Labour also wins a majority.
What we might see during the 1980s is a tendency for the main parties to fracture across national boundaries. In Scotland, the governing Labour group avoids the leftward drift of the national party (there is no SDP in Scotland for example) while the Scottish Tories split between the anti-devolution Thatcherites and the pro-devolution "wets". This latter split becomes a schism with the coming of the Poll Tax. The Scottish Thatcherites under Michael Forsyth back the Poll Tax in 1987 leading to a mass breakaway by traditional Scottish Conservatives, some of whom join the SNP and some the Liberals. The Scottish Labour party breaks away from England as early as 1981 following the election of Tony Benn as Deputy Leader. A number of young Scottish Labour parliamentarians such as Gordon Brown abandon Westminster and use Holyrood instead.
In Wales, events are less dramatic - the Labour Party stays loyal to England but the Welsh Conservatives also split in the late 1980s.
Throughout the 1980s, Labour controls the Welsh and Scottish Assemblies but in the 1989 elections, the Scottish Labour Group loses control after a series of financial scandals. An SNP/Green coalition takes over and holds a refrendum on independence. The vote is won by 58% to 42% but the result is not recognised by Mrs Thatcher or her Scottish Secretary, Malcolm Rifkind.
Tensions run high until Thatcher falls in November 1990. The SNP administration also falters and in 1993 Labour is returned under Gordon Brown. Though not in favour of full independence, the new Government wants much greater power for what it calls the Scottish parliament. This finds an echo in Wales but John Major refuses to change the status quo of 1979 which gave only limited powers to the devolved assemblies.
Tony Blair becomes Labour leader in 1994 and Prime Minister in 1997. Initially, all goes well and considerable powers are passed over to the Scottish Parliament and Welsh Senedd in the first months. Some English regions, especially in the north, want some kind of devolution too as does London.
Tensions increase in the first Blair Government and its re-election in 2001 does nothing to quell rising concerns in both Scotland and Wales that Labour is not going to deliver full devolution. Under veteran leader Alex Salmond, the SNP forges a new coalition with the Scottish Liberals and Scottish Conservatives and this group wins the 2001 Assembly elections. In Wales, too, Plaid Cymru and the Liberals end more than 20 years of Labour rule and take power on a "full devolution" platform. Blair initially refuses to give away but the Iraq War of 2003 proves disastrous in domestic terms. Huge anti-war demonstrations in Glasgow, Edinburgh, Cardiff and Swansea lead to further schism within the Labour Party in the English Regions as well as elsewhere.
It is, however, fuel that precipitates the final disaster. Rising fuel prices in 2004 lead to a fuel price protest and when officials in London complain that the Scots and Welsh are not acting quickly enough to break the blockades, there is outrage. With the Scottish police apparently supporting the fuel protesters, the Army is ordered to Grangemouth to open the refinery. The police bar the way and a standoff ensues. With the fuel crisis mounting in England and Wales, Defence Minister Geoff Hoon orders the Army to break the Grangemouth blockade. When police and protesters try to intervene, there is violence and three people are killed. This leads to a surge of anti-English hysteria across Scotland into which the Government is soon swept along. Alex Salmond calls for calm but Jim Swinney takes over in a coup within the SNP coalition and, backed by the Greens and Scottish Socialists, calls on police and lorry drivers to block the M74, A66 and A1 roads at the border.
In London, there is panic and army units are dispatched from Catterick to re-open the roads. However, Swinney calls on Scots to "defend the motherland" and the Army units are met by small-arms fire at Gretna and Carter Bar. Tanks soon break through but face civil disobedience from indignant Scots. The English media is screaming that civil war has broken out and further south Welsh protesters cut the M4 and A5 roads in sympathy.
As England slides into anarchy, the northern English Regions offer the Scots and the fuel protesters their support. Demonstrations in Durham and Carlisle call openly for independence from London and in Edinburgh John Swinney, in front of thousands of cheering Scots, proclaims an independent Scotland even as RAF jets fly overhead.
Late that night, Hoon receives word that Scottish regiments have refused to march north and that fighting between English and Scottish soldiers has broken out in Iraq and elsewhere. In London, pubs known to be frequented by Scots are attacked and two Scots are lynched in ugly rioting in Birmingham.
Two days later, Blair proclaims a State of Emergency but the protesters are now in effective control of Newcastle, Durham, Carlisle and Bristol. In Edinburgh, Swinney and the Scottish Militia control the major towns and cities. In the midst of the crisis, there is a summons from the Queen. Details of what was said at the Audience are never revealed but Tony Blair resigns at 9pm that evening. An all-party coalition takes over led by Liberal Democrat Menzies Campbell. Campbell is hugely respected in Scotland and he arrives two days later to a warm welcome. He has come to redraw the constitutional map of Britain. The fuel protests are suspended and the borders are re-opened.
Six months later, Britain has changed. Scotland is an independent state within the EU and the Commonwealth. Prime MInister Jim Swinney heads a broad Coalition which faces a series of tough decisions as the financial lifeline from England will be turned off in 2012 and oil production is already past its peak. Wales too is independent though still economically bound to England. Cumberland, Northumberland and Durham are joined in the Northern Region Assembly while Yorkshire has its own Assembly as do London, Birmingham, Liverpool & Manchester and Cornwall. Politically, much as changed in England with a Tory-Lib Dem Coalition managing the transition from a state of nations to a true nation-state.