Leading article: Everyone lives to fight another day, but the real test is still to come

The result of the Oldham East and Saddleworth by-election offers varying degrees of comfort for each of the main parties.

Obviously, Labour has most cause to celebrate, winning the seat by a substantial margin. Last year, as the general election moved into view, some senior Labour figures feared meltdown in the aftermath of defeat. Instead, Labour proved itself to be a convincing fighting force in a potentially awkward by-election, retaining some of the hunger for victory that distinguished New Labour under Tony Blair.

By-elections early in a parliament tend to have little long-term relevance. On the surface, the outcome here continues the trend. The main opposition party beat the two parties that form the Coalition. Governing parties rarely win by-elections, especially when implementing unpopular policies.

Still, this was the first contest since the Coalition secured power and Ed Miliband became leader of the Labour Party. The victory will give Mr Miliband some momentum and political space after a period punctuated by murmurs of internal discontent. Nick Clegg also lives to fight another day after a period in which some have predicted the near-demise of his party. If the Liberal Democrats had come third, a sense of crisis would have overwhelmed them, threatening the stability of the Coalition. This will be a source of some comfort to David Cameron, too: the Coalition has survived the by-election. Evidently some Tory supporters voted tactically in the hope of preventing Labour's win.

These switches explain why this by-election might prove to be an important marker. Presumably Labour benefited from the support of disillusioned Liberal Democrats, while Tory voters felt able to give Mr Clegg a helping hand. By the next general election will the Liberal Democrats' leadership lean rightwards in an attempt to appeal to Tory voters like those prepared to vote tactically in the by-election? Is there still a distinct section of voters who are liberal and Liberal Democrat? The tentative, provisional, moves made by voters in Oldham East and Saddleworth may point to a deep shift in British politics in which Labour becomes the single national party of the centre left and the Liberal Democrats sink or swim, depending on the mood of voters more inclined to support the Conservatives.

Beyond these ripples the by-election is much less important than the electoral battles soon to come. The local elections this May represent a much bigger test for the Coalition, and for the Liberal Democrats in particular. Mr Clegg's party is formidably strong in local government and will be defending seats this May just as the sweeping cuts in council funding take hold.

The local elections also coincide with the referendum on the alternative vote, after which Coalition unity will be truly tested, whatever the outcome. A "Yes" vote will give the Liberal Democrats hope and alarm parts of the Conservative Party. A "No" vote, along with bad local election results, would plunge the party into crisis. Meanwhile, Labour must prepare for the phase in this parliament when it is judged as an alternative government, not a vehicle enabling voters to protest painlessly against the policies of the Coalition. Can it rise to the challenge? The by-election raises more questions than answers in an already unusual and febrile political situation.