Prime ministers invariably make a mess of Cabinet reshuffles. Tony Blair was rotten at them, succeeding only in creating resentment among those shifted. Now the first big test of Gordon Brown’s political authority after the Manchester conference will be whether he changes his team and, if so, how.

As ministers moved from meeting to meeting, and meal to meal, gossip circulated about whether Mr Brown would try to get rid of some of his critics and promote allies. The favoured dates are the Thursday and Friday of next week, October 2 and 3, after the end of the Conservatives’ Birmingham conference.

The central question about all reshuffles is whether they make any difference to the effectiveness of the Government or to its standing with voters. Most do not since they involve merely shifting around ministers of whom the public has never heard.

There are three categories of reshuffle: first, the mega, involving the Chancellor or Foreign Secretary; second, the midi, purging and promoting other Cabinet ministers; and, third, the mini, peripheral moves in and out, and changes in the machinery of government.

A mega shuffle is the riskiest. Mr Brown looks more secure today than he did, say, a fortnight ago. But is he strong enough to change his team without provoking opposition that could destablise him? Alistair Darling is still apparently vulnerable, though moving him would be extraordinary at such a sensitive time in financial markets, especially when the key decisions have been taken jointly with Mr Brown. Moreover, as he showed in his conference speech yesterday, the Chancellor has a sure and reassuring style. And any replacement might be seen as a rival or a crony.

Similar dangers apply to a midi shuffle if Mr Brown sought to purge the likes of Ruth Kelly, Hazel Blears and even James Purnell, the successful Work and Pensions Secretary, as one lurid rumour yesterday suggested. Such a move could easily provoke Cabinet members into outright revolt. Mr Brown would be wrong to assume that the public display of ministerial loyalty this week is any more than conditional, and remains dependent on what he does.

A mini shuffle will happen soon anyway. Lord (Digby) Jones of Birmingham is due to depart soon after an unsuccessful 15 months. Of more importance, the long-mooted creation of a department for the nation and regions - incorporating the Scotland and Wales Offices, and possibly also the Northern Ireland Office - may eventually happen. Jim Murphy, the Europe Minister, who handled the Lisbon treaty Bill skilfully, is tipped to get the appointment.

For all his global and strategic insights, Mr Brown is a notoriously cautious politician. He has regained the initiative, at least temporarily, over his divided critics. But a botched reshuffle could end the current public truce and reopen the warfare in a more damaging way.

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