One of them, possibly both, is going to end up a loser

Given that the British electorate as a whole only gets to vote once every 4-5 years, it is perhaps inevitable that by-elections tend to wield a somewhat disproportionate influence on our political process.

Usually they follow a fairly predictable pattern. The public – or the media – identifies which of the two main opposition parties is most likely to give the governing party a good kicking, and the 'protest vote' does the rest.

But we are in unchartered waters now. There are two governing parties, only one main opposition party, and the new-ish leader of that party is something of an unknown quantity to most voters.

All of which is what makes Thursday's Oldham and Saddleworth by-election possibly the most fascinating such encounter since the Darlington contest of 1983 which, to Labour's ultimate detriment, saved the leadership of Michael Foot.

On the face of it, it ought to be plan sailing for Labour. In a few short months, the Con-Lib coalition has slashed public spending, put up VAT, and scrapped much of the regional aid budget that was helping former industrial towns like Oldham to find a new role.

Not only that, but the seat was won by Labour in the general election last May, before MP Phil Woolas was disqualified from Parliament for having lied about his Lib Dem opponent on his election literature.

One of the many imponderables in this contest is whether the fate of Mr Woolas will help or hinder Labour's cause here.

The fact that he was actually quite a popular local MP might appear to favour the party, but some voters may feel he was too readily hung out to dry by the Labour establishment, and punish the party accordingly.

Inevitably given its status as a three-way marginal, 'Old and Sad' is being viewed as something of a mini-referendum – not just on the Coalition, but on Labour leader Ed Miliband.

If Labour cannot even win by-elections in seats it already holds, serious questions will start to be asked as to whether it can win anywhere else under Mr Miliband's leadership.

But for Lib Dem leader Nick Clegg, too, a defeat on Thursday would be seen as a significant blow.

His party's candidate, Elwyn Watkins, may well feel the seat is his by moral and indefeasible right having been on the wrong end of Mr Woolas's misdemeanours, but politics doesn't work like that.

Undoubtedly the leader with the least to lose and the most to gain here is Prime Minister David Cameron.

For one, the Conservative candidate Kashif Ali started the contest in third place. For another, the Tories have been accused of soft-pedalling their campaign in a bid to help their Lib Dem partners.

Perhaps realising he is in with an outside chance of a stunning victory Mr Cameron is now doing his best to dispel that impression, becoming the first premier to campaign in a by-election for 13 years.

Yet ironically a Tory win, in a seat where the Lib Dems began as the main challengers, might end up being more destabilising for the Coalition than a Labour triumph.

Mr Clegg would then face more tough questions from his own activists and MPs as to what exactly the Lib Dems are getting out of the Coalition.

A Tory victory would simply reinforce the idea that it is the Lib Dems who are taking all the political pain while Mr Cameron reaps the political dividends.

But whoever wins on Thursday, at least one and possibly both of Mr Cameron's fellow party leaders are going to be waking up to some difficult headlines on Friday morning.

And for either or both of them, that could set the tone for a tricky political year ahead.

Why 2011 is the Coalition's make-or-break year

Two weeks ago I concluded my review of the political year 2010 by posing a question which will, in my view, determine how the next 12 months in British politics ultimately pan out.

It was: can the Coalition government as a whole withstand the dramatic loss in popularity suffered by the Liberal Democrats since their decision to go into partnership with David Cameron’s Tories.

As Ricky Ponting can no doubt testify, a team is only as good as its weakest link, and with public support for the Lib Dems now barely registering in double figures, Nick Clegg’s party are clearly the weakest link in this government.

The big question for Mr Clegg is how much lower he can afford to allow that support to drop before continuing membership of the Coalition simply becomes politically unsustainable.

If any further proof were needed of the Coalition’s inherent instability, then the Vince Cable affair in the run-up to Christmas surely provided it.

There were several ironies about this episode, not least that a newspaper which shared Dr Cable’s hostility to Rupert Murdoch’s takeover of BSkyB managed to shoot itself so comprehensively in the foot.

But surely the biggest irony of all is that, for all the humiliation he heaped upon himself, Dr Cable turned out to be correct in his estimation that he was, in effect, unsackable.

Whatever you think of the methods used to ‘entrap’ him, any other minister who displayed such appalling naivety and lack of judgement would surely have been out of the door.

But because Mr Cameron dare not weaken the Lib Dem element of the Coalition for fear that the whole edifice will collapse, he survived - thought not without having his wings severely clipped.

So much for the events of the week before Christmas. What of the year ahead?

Well, since this is traditionally the time of year for crystal ball gazing, I’ll make a prediction. If the Coalition gets through the next 12 months, it will more than likely achieve its ambition of serving a full five-year parliamentary term.

Why is 2011 likely to prove the Coalition’s make-or-break year? Well, for starters, it is likely to become significantly more unpopular as the cuts bite, unemployment continues to rise, and the full implications of some of its more radical experiments become clear.

I have in mind here Andrew Lansley’s NHS reforms and Michael Gove’s de-municipalisation of schools, neither of which can claim much of a popular mandate.

But the biggest single threat to the Coalition’s survival is the time-bomb that is due to detonate underneath it on Thursday 5 May – the referendum on the alternative voting system.

If, as many now expect, the referendum is lost, it will remove the Lib Dems’ main incentive for having entered the partnership in the first place.

For Labour leader Ed Miliband, too, this will be a critical 12 months, as he seeks to demonstrate to a sceptical public why he, and not his elder brother, is the right man for the job.

At least he now has a clearer opposition strategy, seeking to brand this a Conservative-led government supported by reluctant Liberal Democrats rather than the marriage of true minds Messrs Clegg and Cameron would like to portray.

Yet for all that, Mr Miliband is probably no more keen to bring the government down right now than Dr Cable: his party is broke, he hasn’t had time to overhaul the policies that lost it the last election, and the public doesn’t really know him.

If the Coalition does manage to survive the year, it might simply be because none of the three main parties really wants to have another election just yet.

Review of the Political Year 2010

When future historians come to assess the political events of 2010, two big counterfactual questions are likely to loom large in their minds.

They are: what if Labour had ditched Gordon Brown before the General Election, and what if the Liberal Democrats had refused to go into coalition with David Cameron's Conservatives?

The second question is probably the easier one to answer. Mr Cameron would have formed a minority government, David and not Ed Miliband would have become Labour leader, and both would now be gearing up for a fresh election in the spring.

But the more tantalising question is whether Mr Cameron might never have become Prime Minister at all had Labour gone into the election under a more popular leader.

The political year 2010 began with Mr Brown's survival once again hanging in the balance.

Former Labour ministers Geoff Hoon and Patricia Hewitt attempted to get MPs to demand a leadership contest, but rightly or wrongly, the consensus in the party was that by then it was too late to change horses.

As it was, the election turned into a slow-motion car crash for Labour, dominated by televised debates in which Mr Brown was predictably outshone by his two younger, more charismatic opponents.

Then, in the final week of the campaign, came 'Duffygate' - the kind of incident which could have happened to any of them, but which seemed somehow fated to happen to the luckless Mr Brown.

In terms of issues, the campaign centred mainly on the question of how to deal with the country's biggest budget deficit since the 1930s.

Here Labour was on an equally sticky wicket, with voters clearly concluding that the party was 'in denial' about the extent of the problem and crediting the Tories for being at least partially honest about the scale of the forthcoming cuts.

For all that, though, the public remained largely unconvinced by Mr Cameron and his team, and the eventual result saw the Tories falling some 20 seats short of outright victory.

Days of frantic bargaining followed, but with the parliamentary maths in favour of a Lib-Lab deal failing to stack up, it was always likely that a Lib-Con coalition would be the outcome.

Faced with the task of finding a successor to Mr Brown, Labour managed to saddle itself with the lesser-known of the Miliband brothers, courtesy of a crazy electoral system which gave the unions the decisive say.

For David Miliband, brother Ed's leadership election victory came as a bitter blow and the South Shields MP stood down from his party's frontbench.

Then, in one of his first acts as leader, Ed sacked former Minister for the North-East Nick Brown from his Shadow Cabinet team, leaving the region somewhat leaderless in Whitehall.

Indeed, with the new coalition busily taking the axe to every regional institution in sight, the North-East seemed in danger of losing its political voice altogether.

Initial excitement about the coalition soon faded. The 'new politics' spoken of by Lib Dem leader Nick Clegg in the TV debates soon regressed into the old politics of broken election promises.

Chancellor George Osborne had expected that the £80bn programme of cuts unveiled in his October comprehensive spending review would swiftly make him the most unpopular man in Britain.

Instead, it was Mr Clegg who became the government's fall-guy, completing his journey from hero to zero by backing the rise in tuition fees against which he had so vehemently campaigned in April and May.

The Lib Dems' decision to trade principle for power has clearly come at a huge political cost. The key question for 2011 is whether the coalition as a whole can survive it.