Mr Brown has said wage inflation 'discipline' is vital

General secretary Brendan Barber said giving a 2.5% rise in two separate stages would hurt NHS and civil service morale, reducing support for Labour.

The warning comes after a recent strike by prison staff and arguments with nurses and police over pay.

Mr Brown has said the settlement is "an essential part" of tackling inflation and keeping the economy stable.

An independent pay review body recommended a 2.5% pay rise but the government staged this, awarding 1.5% in April and the remaining 1% from November.

'Real resentment'

Unions say awarding it in two stages makes it worth 1.9%.

In a briefing ahead of the TUC annual congress in Brighton next week, Mr Barber said: "Millions of public sector workers who work with dedication and commitment feel real resentment and anger at the way the government this year have tried to railroad through a rigid, unjustified pay limit well below the rate of inflation."

He added: "Of course, unions well remember the bad old days of inflation, but we know of no respected commentator who thinks public sector pay is the engine that led to upwards pressure on inflation."

Mr Barber said it was wrong that "no action" was taken to reduce "billions of pounds worth of City bonuses and boardroom excess that do feed straight into house prices".

He warned that Mr Brown could not "afford a repeat of this next year".

'Signals'

Mr Barber also said: "Rather than public servants feeling they can act as positive ambassadors for the changes in public services, they feel very negative.

"One of the things that matters most is the signals people pick up from staff in the public services.

Mr Barber said public sector workers felt resentment

"The government is paying a political price as well as an industrial price in terms of morale."

But Mr Brown, who decided to stage the pay rises when he was chancellor, said last week: "We have succeeded in tackling inflation and having a stable economy because of discipline in pay over the last 10 years. That discipline will have to continue."

He added that staging pay awards was an "essential part" of controlling inflation, keeping interest rates low and creating more jobs.

He said: "We will do nothing, nothing, to put that at risk. It is an essential element of maintaining discipline in the economy."