The FBU said it members felt betrayed by a lack of progress in their ongoing dispute over pay and conditions.

The Scottish Trades Union Congress (STUC) will hear more about the findings at their conference in Inverness.

Bill Speirs, the STUC general secretary, told the BBC's Good Morning Scotland programme that the findings were very worrying for Labour.

"It's a measure of the extent to which this dispute has not been well handled by the government," said Mr Speirs.

Deal

"It actually started when the STUC was gathering in Perth a year ago; that was when the original claim was formulated by the union.

"We can only hope that some sense can prevail, a deal was actually done on the seventh of November last year between the employers and the Fire Brigades Union which was then sabotaged by John Prescott."

But a spokesman for the Scottish Labour Party told BBC News Online Scotland: "Labour has delivered and will continue to do on the priorities of the trade unions.

"I expect on 1 May that trade unionists will vote to continue with investment in the public services we all rely on and not for the Nationalist's expensive divorce."

Meanwhile, the STUC conference is expected to fiercely condemn the war in Iraq during the longest debate at annual congress for at least a decade.

Iraq war

Organisers have torn up the congress agenda to give angry delegates three hours to voice their opposition to the conflict.

The debate was centred around a statement from the STUC's general council which insisted that the war "did not have to be fought".

And it said the conflict was a war which had "cost thousands of innocent lives and whose consequences will be literally incalculable".