Projecting into the future, let's say Scotland votes No in the referendum (which seems highly likely), which puts the dampers on secession for a generation. Salmond is replaced by a less 'jocular' leader who focuses the SNP on getting more powers and privileges for Scotland within the Union and acting as the only real opposition to Labour in the country.
Labour wins respectably at the 2015 general election, and the Conservatives are removed completely from the Celtic fringe.
Let's be nice to Miliband and say the global economy picks up around the same time, earning Labour undeserved economic kudos. Wales get a full Parliament during this period and devo max is introduced in Scotland. Growing interest in English devolution sees only minor concessions, granting city governments more power and networking council of the big cities, primarily Labour run.
Labour wins again in 2020, with many of their losses being compensated by the continued decline of the Liberal Democrats. This causes some headaches at Central Office and the Tories undergo some soul searching. However Labour comes under attack over its unsure position to EU federation.
This decade of Labour rule, which is apparently anti-English leads to growing support for groups like the English Democrats, nothing substantial in terms of power but their vote share jumps up, taking large chunks out of the BNP and UKIP bases.
In time for 2025, influenced by growing English nationalism, a new Conservative leader promotes a platform based on ending the 'subsidising' of Wales and Scotland and granting England its own powers. This is done to great anger from Cardiff and Edinburgh by this point both back under the control of the nationalists. A crisis of sorts blooms as thousands of civil servants are laid off and budgets slashed.
Promoted by the tabloid press and genuine popular support in certain areas of England, an English Parliament is created, and a Conservative-*English Democrat coalition in charge.
Secessionist support rises once more in the regions, but this time is joined by support in England to 'dump' the Welsh and Scots who take more than they give. Labour supports takes a Unionist line but large sections of the party in Wales and Scotland are backing secession, while the economic problems of the second Miliband term is still felt, weakening their power in England.
In a fit of pique the PM calls for an English referendum earlier than the Scottish and Welsh ones, officially calling for the 'people to be heard' but by now the Tories are seen as an English party and many members, particularly younger one with little British patriotism campaign for English secession. The referendum also acts as a poll on Europe and federation as a free England will not be an EU members. Europhobia, Celtophobia and English patriotism abound.
In July 2029, England secedes from the UK, causing it to collapse as a sustainable entity within the year.
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not mind blowingly realistic but I imagine sustained anti-Union feeling will eventually lead to an English back lash of some sort.