The Liberal Democrat conference slogan "fairer taxes in tough times" set a sombre mood.

With his party's unpopularity confirmed in every opinion poll and his own rock-bottom rating at embarrassing levels, Nick Clegg yesterday had no option but to outline the absolute necessity of continuing to back the Conservatives' austerity measures while seeking to sweeten the medicine where the party could.

He had very little to offer on that front. The only commitment he could make to the fairer-taxes mantra was that there would be no further reductions to the top rate of income tax below 45% in the current Parliament. The long-standing LibDem policies for a mansion tax and additional bands above the top rate of council tax remain aspirational.

Despite the muted tone and the emphasis on the need for austerity and belt-tightening in the "gargantuan task of rebuilding the economy", Mr Clegg's political strategy rests on hope. His claim the LibDems are the only party that can be both trusted on the economy and relied upon to deliver a fairer society will find traction with voters only when the economy has turned the corner sufficiently to demonstrate that cuts were justified and LibDem measures were ameliorating their impact. It was obvious from the careful avoidance of how this could be achieved that it will be difficult for the LibDems to point to how they have put social democratic principles into effect. A commitment to begin tax reform at the top lacked detail. The statement by the Chief Secretary to the Treasury, Danny Alexander, that £16 billion of public spending cuts would be required in the year 2015-16 suggests the squeezed middle is likely to suffer further and opened an unwelcome debate on currently protected universal payments such as winter fuel allowance for pensioners. Their best hope is that measures for which they claim credit, including the green bank and the business bank, take effect soon enough to boost growth through increased infrastructure spending. But Mr Clegg's declaration that the party's mission is national renewal was woefully short on substance. To the outside world, it lacked credibility.

The list of LibDem achievements party activists could boast about, such as raising the tax threshold and the pupil premium in England, was more a recognition that they face a negative reception on the doorstep than a rallying call for the benefits of oalition government. That the most positive reaction was to the announcement that Paddy Ashdown is to lead the 2015 election campaign suggests confidence in Mr Clegg remains low.

The test will be whether voters in 2015 will see the LibDems as having sufficient clout to hold either Tories or Labour to the centre ground. The omens are not good. Mr Clegg sought to outline a meaningful future for the LibDems, not as the third party but one of three parties of government. The prize for LibDems is another term in coalition government. Few outside Brighton are convinced they deserve it.