Inevitably it will help to bring to a head the fears of the remaining One Nation and pro-European Tories in Mr Major's ranks, who have become increasingly disillusioned at the Conservatives' rightward and anti-European drift. Despite their claims to have a majority in the parliamentary party they have proved themselves unable to modify the Government's isolationism in Europe and its harsher rhetoric and policies at home. Now more will have to decide whether to stay and fight, or abandon a Conservative Party which if it loses the next election looks set for a battle that could come to match the internal divisions that Labour faced in the early Eighties.
But if it is bad news for the Conservatives, it is bad news too for the governance of the country. Mr Major's majority is now down to five, and is likely to fall to three after the two pending by-elections. It will take only another couple of defections - or, more probably, the likely death of a couple more Conservative MPs - for the Prime Minister, on recent by-election form, to be heading for a minority government later this year and all the special trading with special interest groups that this is likely to imply.
The Prime Minister will be increasingly reliant on Ulster Unionist votes or abstensions to carry his business - a prospect which will threaten the one undeniable achievement of Mr Major's premiership, the Ulster peace process. An already weak government is set to become even weaker, with the Prime Minister having to tack ever more frequently, first to his party's left and then to its right, in an attempt to hold his government together.
Ms Nicholson's defection may not be unmitigated good news even for the Opposition. Tony Blair has undeniably changed his party's rhetoric and direction (not least by claiming for Labour the One Nation mantle that Ms Nicholson and Mr Howarth believe that the Conservatives have abandoned). But new Labour still has big questions to answer: over future welfare policy; on how, beyond a windfall tax, it will fund its jobs and training programmes; on how it can square its claims to be a party of low taxation with the funding of a modernised welfare state.
Faced by what looks increasingly like disintegration on the Tory benches, Labour may be tempted to put off the hard answers. If that were to happen, Ms Nicholson's defection will have done the Opposition and the country no favours, reducing the chances that when an election does come, the electorate will have on offer a fully coherent alternative to the Conservatives.