Win or lose in Glasgow, Mr Brown will remain Prime Minister and Alex Salmond will retain the initiative in Scottish politics. But what is being called Warwick 2, after the original deal with the unions there in 2004, will have a crucial bearing on Labour's future. This is less about immediate policies than what is said at the next election and, even more crucially, afterwards, especially if Labour loses. Mr Brown will want to avoid a row by seeking agreement on “family-friendly” policies (though business will watch the costs), on making the economy greener and on improving skills. Mr Brown has opposed any return to the past on union rights and John Hutton, the Business Secretary, is strongly resisting changes to labour laws and regulations that would threaten the competitive position of British business.

There have been two big changes since 2004. First, the Labour leadership is much weaker, politically and financially. The party has huge debts, and has become dependent once again on the unions for the vast bulk of its funding. Secondly, the government side is not united. While there is agreement that no ground should be given on labour laws, there is pressure from some advisers to compromise with the unions on other issues. The key ministerial figures are Pat McFadden, who managed liaison with the unions for Tony Blair, and Ed Miliband, the Cabinet Office Minister who is in charge of Labour's manifesto preparations.

There have been tensions between the officials and ministers friendly to the unions, and Mr McFadden and departmental ministers, keen to ensure no dilution of their reforms. Union leaders do not want to push the Government too far in public for fear of weakening Labour and strengthening the Tories.

The stakes are high for Mr Brown. First, any policies that increase regulations or costs will aggravate relations between the Government and business. Secondly, any impression of giving in to the unions would be immensely damaging to Labour's image and prospects. Expect plenty of fudging, but watch for a shift in the balance of power.

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