Leading article: Union loyalty to the PM shows signs of fraying

The annual conference of the Trades Union Congress opens in Brighton today with a varied agenda but one that is bound to be overshadowed by continuing speculation about Gordon Brown's leadership. Although unions clearly do not wield anything like the same power within the Labour Party that they did 30 years ago, when they all but terrorised the governments of Harold Wilson and Jim Callaghan, they remain a significant force, not least because of their financial donations. Their voice is important when doubts arise about the party leadership.

These tensions within the party have already manifested themselves in pre-conference interviews, in which some senior union leaders have attacked the Foreign Secretary, David Miliband, who is widely seen as a rival and potential successor to Mr Brown. This is not surprising. Even in more challenging times than these for Labour, union leaders have historically rallied round the party leader and been wary of attempts by others to remove him.

In this case, although the unions have deep policy differences with Mr Brown, most are likely – at least in public – to declare their support for the embattled leader over any alternative. Indeed, judging by some comments at the weekend, any attempt at regicide will prompt an angry reaction from sections of the unions; it is another reason why, beyond Charles Clarke and a handful of others, there is no real momentum at this point behind the push for an alternative leader to Mr Brown, in spite of the party's dismal poll ratings.

While the rumblings of irritation aimed at Mr Miliband point to the risks involved for Labour in seeking to dethrone Mr Brown, all this could change in the coming weeks if the Prime Minister's attempt to relaunch himself politically is judged to founder. In the end, failure on that front could persuade even hardened Brown loyalists in the unions that his time is up. Equally, it is evident that the unions have not reached that point yet.

While any suggestion that union leaders are part of the much talked-about "plots" against Mr Brown's leadership will be eagerly seized upon, this week's policy debates will be at least as important in terms of the unions' future relations with the Government.

Here, the unions will be at odds with the Government on several fronts, from strident calls for tax increases on the so-called "super rich" who earn more than £100,000 a year, to enthusiasm for a one-off windfall tax on energy companies and demands for generous pay awards in the public sector. With inflation running at 4 per cent, the Government's determination to hold public sector pay increases at 2 per cent is causing palpable anger.

But while the differences between unions and the Labour leadership are wide and deep on most of these issues, such differences are par for the course, and ever since Labour came into office in 1997 there have been similar tensions with the unions. The difference, this time round, is that they meet in worse economic circumstances than in any year since 1997. But that gloomy economic backdrop also means ministers can argue with good cause that their hands are tied.

Questions relating to the leadership of the Labour Party and the future direction of the Government will not be decided this week at Brighton. But as an opening to what looks like being a febrile conference season, the events in Brighton will certainly mark an important salvo, and they suggest, as many expected, that the next few weeks will be highly charged for Labour.