Next week Scotland will vote on independence. No matter the outcome, the result will be more federalism in Great Britain. Even if Scotland votes nae, that vote will still probably be close. And much like what happened in Canada with Quebec, Parliament will have to give Scotland more autonomy to prevent a future vote from going the other way. (Indeed, a proposal of this sort is already being floated to sway undecided voters.) If Scotland votes aye, then one would expect Wales to demand and get more autonomy to stay in the Union, though Wales is a less viable independent states.
One curiosity about the upcoming vote is that Britain is due to hold a general election next year. If Scotland votes aye on independence, then would it still get to vote in that election? It will probably take more than a year to finalize Scottish secession, but it would be weird if a departing part of the country gets to form a new government. (And then, I guess you’d have to have a new election as soon as all of the Scottish MPs leave.) Of course, Parliament could simply postpone the election (something that cannot be done under our Constitution), but that creates its own difficulties.
One last thought. At what point will a federal Britain need an English Parliament as distinct from Westminster? In other words, right now there is no English provincial government–there are only national, Scottish, Welsh, and local ones. How long is that sustainable if Scotland and Wales get more power within Britain?