Michael Brown: Lib-Dems can try and turn themselves into Tories, but I fear they'll still be squeezed out

If Vote Blue, Go Green was the new Tory slogan introduced by David Cameron, is Nick Clegg's Liberal Democrat party now inviting us to "Vote Lib-Dem, Go Blue"? Yesterday's tax-cutting announcement by Mr Clegg was either a thoroughly irresponsible ploy by a third party – with no chance of winning the next election – to garner cheap votes by making promises it will never be called upon to redeem, or a serious attempt to outflank the Tories as the real party of tax and spending cuts.

But with the prospect of a hung parliament now receding, and in the wake of Mr Cameron's consistent 20 per cent poll lead over Labour, the Lib-Dems may secretly feel the luxury of populism without a price tag is the best way of staving off the Tory threat to their own seats in Middle England.

Political cross-dressing has become infuriatingly confusing for voters since the advent of Tony Blair. By 2005 it was commonly perceived that left-inclined voters were more likely to be attracted by Charles Kennedy's anti-Iraq war stance. The general perception, recorded by opinion polls at the time, was that under his leadership the Lib-Dems – pledged to increase the top rates of tax – were seen as a party well to the left of New Labour. With the country still in an anti-Tory mood, the Lib-Dems became an attractive alternative for Labour voters who did not want a change of government but who wanted to register their dislike of Blair and the Iraq war.

Mr Clegg's repositioning of his party has also to pass the test of credibility among his own activist members who, from my observations after attending a decade of Lib-Dem conferences, certainly appear to have been even more wedded to the concept of higher public expenditure and progressive taxation than even Labour activists.

The forthcoming party conference will now be a test to see whether Mr Clegg has the authority to change his party's mindset. Lib-Dem conferences remain the formal policy making forum that must approve the leadership policy programme. They are notoriously difficult platforms on which the party leader can perform political somersaults of this audacity.

In 1997 there was no doubt that the Lib-Dems, under the leadership of Paddy Ashdown, were part of the informal national anti-Tory political consensus. The Lib-Dems were central to the "get the Tories out" movement led by Tony Blair. Ashdown never sought to disguise his view that the Major government should be thrown out of office. And, while deals were denied, there is no doubt that the "tactical vote" strategy was operated on an informal basis between Ashdown's and Blair's respective party machines across dozens of constituencies.

The question that is now explicitly raised for Mr Clegg, as he poses as more Tory than the Tories so far as tax-cutting is concerned, is whether he is willing to be seen as part of the wider Tory campaign to get Gordon Brown and Labour out of office. I have the privilege, from time to time, of interviewing Mr Clegg, as a Sheffield MP on the Yorkshire TV regional politics programme which I present. So far, he has successfully evaded all my attempts to pin him down as to whether he would prefer to see Mr Cameron replace Mr Brown as prime minister at the next election.

Of course, when his party was securing poll ratings above 20 per cent (and with the evidence initially pointing to a hung parliament at the next election) he could, with good reason, evade this question by using the well-rehearsed formula of supporting, in the division lobbies, either main party on a case-by-case political issue.

That answer is progressively unlikely to satisfy voters, who seem to have decided that they want to throw Mr Brown out. Maybe yesterday's Lib-Dem announcement to reduce the standard rate of income tax to 16p in the pound to be paid for by £20bn of public expenditure is a recognition that even this once high-spending party has glimpsed the new mood of voters who, while tightening their own budgets, are in the mood for similar economies by government and who don't appreciate Mr Cameron's apparent, but understandable, caution.

The battle lines between Mr Clegg – who stands to lose dozens of seats, won since 1997, back to the Tories – will come down to one of credibility. The Tories are still scarred by their own lack of credibility in 2001 and 2005 when tax cuts at the expense of public expenditure savings caused them so much difficulty.

Paradoxically, the darkening economic storm clouds make it easier for Mr Cameron to resist the Tory activists' calls for early tax cuts. Even the revered Geoffrey Howe has recently reminded us that in 1979 the Labour legacy required the early Thatcher government to restore the public finances with substantial tax increases. With declining revenues from VAT, stamp duty and corporation tax, the U-turns over fuel duty and the 10p tax debacle, the fiscal deficit likely to be bequeathed to the Tories will probably now prohibit any overall tax cuts in George Osborne's first budgets.

If Labour resort to allowing the borrowing requirement to burgeon in response to backbench calls for a further U-turn over vehicle excise duty, the question of tax rises, rather than cuts, will overshadow the new Tory chancellor's room for manoeuvre.

Where, however, Mr Clegg may have overtaken the Tories is in reading the new mood of voters for public-sector austerity. The Tories – trapped by their past unhappy experiences – are determined not to be painted into a corner as a party of "cuts". But new circumstances suggest that the public may believe that austerity measures should not be confined to their own personal expenditure as they face a reduction in their living standards.

If we are being forced to cut our individual household cloth accordingly, why should governments be exempt? Mr Osborne continues to restate the Tory commitment to stick with Labour spending plans, although hopefully a window exists – when the current plans expire in 2010 – for the shadow Chancellor to find the courage to face the demons that blighted the Tories during the last two general election campaigns.

The notion that Mr Clegg will be the party leader most likely to appeal to Tory voters yearning for tax cuts is, nevertheless, still hard to grasp. The Lib-Dems are in serious danger of facing the traditional two-party squeeze. They are a crucial vehicle for Labour in denying the Tories office. But they are an impediment to the Tories when the political pendulum swings in the opposite direction. Their usefulness to the Tories is only if they make inroads in Labour constituencies at a general election. So far, Lib-Dem advances at Labour's expense only occurs in by-elections.

So notwithstanding the Tory caution on economic policy, the prospects of Mr Clegg successfully posing as the leader more likely to out-Tory the Tories seems unlikely to carry credibility. The danger is that the more votes the Lib-Dems retain in what were previously Tory seats, the more chance Labour has of mitigating electoral defeat. Mr Cameron will be determined to prevent Mr Clegg from spoiling the (Tory) party.