By Nick Assinder
Political correspondent, BBC News website
Whatever else happens in 2007 one thing seems certain, at some point Britain will have a new prime minister - even two, if David Cameron gets his way.
The single biggest political event of the year will almost certainly be the retirement of Tony Blair and the selection of his replacement.
Mr Blair's resignation will dominate news
The current betting in Westminster is now firmly behind Gordon Brown taking over in the early summer of 2007, although an earlier date cannot be ruled out.
But Tory leader, Mr Cameron and Lib Dem leader Sir Menzies Campbell, have drawn up contingency plans in case Mr Brown puts himself at the mercy of voters by calling a General Election almost before he has got his feet under the Cabinet table.
They believe it is possible, as Labour chairman Hazel Blears recently appeared to suggest, that Mr Brown could call a snap general election within a short time of replacing Mr Blair in an attempt to validate his premiership with voters, wrongfoot the Tories and secure a full term for himself.
So, 2007 might just be general election year as well. Just don't put a lot of money on it. Politicians never like facing the electorate before they have to unless they believe it is the only way to win - and Gordon Brown will already have "won" the premiership.
There still remains the question of whether a heavyweight, Blairite cabinet member will decide to stand against Mr Brown - with John Reid's name still on some lips despite suggestions he has decided not to run.
Mr Brown may yet face a challenger
Before that day comes, however, there are a number of events that will prove crucial to the atmosphere surrounding his premiership and maybe even the timing.
There is the cash-for-honours police inquiry which may well be concluded one way or another early in the new year. That could have a seismic effect on the government, the political parties and the prime minister himself.
The police have said they will pass a file onto the Crown Prosecution Service in January. If there was any suggestion the prime minister was guilty of an offence, it would almost certainly hasten his departure.
But if there are any charges brought against any Labour individuals, it will send shockwaves through the government and play into suggestions the government is as sleazy as the previous John Major administration was said to have been.
The other big event that could impact on the leadership will be the English local government and Welsh and Scottish assembly elections in May.
There has been some pressure, particularly in Scotland, for Mr Blair to stand down before the polls to boost Labour's standing and head off a possible surge to the nationalists.
But, at the moment, it appears Gordon Brown might be happy to wait until after those polls before taking over the leadership as a "new broom".
Mr Brown will also have to deliver what is likely to be his last Budget in March. It will be scrutinised for signs of what his leadership agenda might be like.
Trident debate and vote will come early
Having said that it will be his big Comprehensive Spending Review announcement in July that will give the clearest idea of what a Brown government will do.
Early in the year there will also be the Commons debate and vote on replacing the Trident nuclear weapons system - something Mr Brown supports but will be happy to see resolved before he takes over.
As for other big policies, while Tony Blair may have mapped out the way forward in welfare, the public services and security - with proposals and votes also due on Lords reform and replacing council tax - nothing will be taken as read until the new leader is in place.
Meanwhile both Tory leader David Cameron and the Liberal Democrats' Sir Menzies Campbell have something to prove over the year.
Both will want to show they are up to the job of taking on the new prime minister and developing policies to boost their standing at the next general election.
Sir Menzies faces a squeeze from any Tory revival and may even hear whispers of a possible challenge to his leadership.
Mr Cameron is planning to finally bring forward more concrete policies after his policy review groups report back.
And, of course, hanging over everything will be the situation in Iraq, and whatever new strategy is devised to withdraw troops without prompting all-out civil war.
The Iraq war and its aftermath still seem set to be Tony Blair's lasting legacy, and he is likely to devote much of his remaining time in power attempting to salvage something from it.
Specifically, he seems determined to do whatever he can to re-start peace moves in the wider Middle East.
So Tony Blair will be hoping that 2007 is the year when there are positive developments towards a more peaceful future for Iraq and the wider Middle East.