Home Secretary Jacqui Smith announced on Thursday that officers in England and Wales would receive a 2.5% increase - but said it would be implemented from December 1 rather than September 1 as expected.

The Police Federation, which represents 140,000 rank-and-file officers, pointed out this in fact represented a pay rise of just 1.9% and threatened legal action. It also warned there was growing support among its members for them to be given back the right to strike.

Police Federation chairman Jan Berry said police authorities and chief constables around the country all agreed the full pay rise was affordable and had budgeted for it.

Failing to back-date the award would leave each police officer about £200 worse off - but she insisted a "greater principle" was involved.

"It's a criminal offence for us to go on strike, or even to talk about withdrawing labour in any shape at all," she told BBC Breakfast. "The one group of workers who have no other opportunity to do this are having this done to them.

"If we were any other part of the public sector, people would be balloting to go on strike. We can't do that. So for me you either have to have industrial rights or you have to have binding arbitration, and we have neither."

Kent Police Chief Constable Michael Fuller said his staff felt "cheated" by the decision not to back-date the pay rise. He said the Home Secretary's position was "regarded as highly insensitive", particularly given that officers in Scotland will receive the full increase.

His colleagues around the country shared his feeling of being "extremely disappointed" by Ms Smith's stance.

Police officers accepted they had "up to now" been fairly well paid, but they faced dangers not experienced by other public sector workers, he added.