But the public service unions are also lining up their own consultants to counter the government's pay experts.

In a rare show of unity in advance of their conferences this week, the three teacher unions - Into, Asti and TUI, representing over 40,000 teachers - have come together to appoint BDO Management Consultants to bolster the union's case for a significant pay rise under the next round of benchmarking pay increases next year. Last time out, the three unions went their separate ways on benchmarking.

Other public service unions, such as Impact and the PSEU, also plan to make combined submissions to the Public Service Benchmarking Body.

Under the last benchmarking exercise in 2002, which awarded �?�1.1bn worth of pay increases to over 250,000 public servants, the government spent almost �?�4m on outside consultants.

Those consultants compared the wages of public servants against comparable private sector jobs and in 2002 concluded that on average public servants were paid 9% less than private sector workers.

But considerable controversy arose when the Department of Finance refused to release the detailed research undertaken by the consultants in order to show how they arrived at a 9% pay gap. This time out Finance has promised more transparency, but publication of the consultants' findings is considered unlikely.