Alex Salmond says he remains determined to have an independence referendum within the next four years - if, that is, he becomes First Minister. However, that determination may not be all it seems.

The prospects of him getting the keys to Bute House look stronger with the start of the year, helped by a rival Labour campaign showing clear signs of anxiety and struggling to deal with the negatives amassed in government, while its MSPs appear to be fighting already over the electoral wreckage and the succession to Jack McConnell.

For the SNP, there is polling data to match, and the party leader may be helped by tomorrow's 300th anniversary of the passing of the Act of Union by the Scottish Parliament, giving airtime aplenty to press the case for its repeal.

But as Labour has long hoped, the SNP's rise means its plans are under more scrutiny and pressure. Its main opponents point to confusion over whether taxes would rise under independence, and the party's defence policy is badly exposed to enemy fire.

This weekend, the pressure forced Mr Salmond to shift his flagship policy of an independence referendum. He says it is only clarification, but that requires a pinch of political salt. The pressure came from his promise to publish a bill for a referendum within 100 days of forming a government.

Labour, including the Prime Minister, deliberately distorted this into a commitment to hold the referendum itself in that timescale. It did enough damage for Mr Salmond to clarify, while moving ground significantly towards potential coalition partners.

The bill will be published, he now says, but it will be within a white paper. The white paper will set out how independence could work, relations with the rest of the UK and with Europe, and it would explain the thinking behind the referendum. It would be a prospectus with which Salmond would enter negotiations with Whitehall. The party will not legislate until it has chosen a referendum date, whereas it could have legislated and decided the date later.

Mr Salmond's comments could be interpreted as meaning the referendum will go ahead only if people debate it and agree with his administration's proposals first. But he claims it would be enough for the SNP to lead an administration from May as a mandate to hold an independence vote.

This was presented yesterday as reflecting the approach taken to the devolution referendum and legislation in 1997 and 1998. The difference is that Mr Salmond looks in no rush to have a vote, as Donald Dewar was back then.

He should be worried by the evidence of his chances of winning such a vote, and they won't be helped from May onwards if Premier Salmond is buffeted from Westminster by Labour's deployment of an arsenal of political weapons with which to undermine his administration.

Although the SNP claims the white paper strategy was published last year, it is no accident it is being highlighted now. If Mr Salmond is in a position to lead coalition talks after May 3, he needs more wriggle-room on the referendum than his party has given him.

LibDem leader Nicol Stephen has set himself against a coalition deal if there is to be a referendum included, and some think Mr Salmond would do well to prove his governing credentials for four years, and he may privately agree. But with signs of movement in the strategy, the Deputy First Minister may have to rethink, if only also in private for now.

Mr Salmond's party will not let him postpone the referendum into the 2011 election. They accepted the idea of a vote on independence because it would make the SNP less threatening to wavering voters: vote Nationalist, but don't worry, because you'll get another chance to vote on independence.

Some hardline nationalists remain quietly unreconciled. They do not want obstacles put in the way of independence, and fear it may derail their cause. They will be unhappy that the new explanation of the strategy gives their leader more room for manoeuvre than they thought they had given him.

But while he rides high, they will probably keep quiet. They know he is a master campaigner and hope he will be as wily a coalition negotiator.