A chief constable has condemned her officers at the centre of a controversy over e-mails offering “premium rates” of overtime in Britain’s biggest anti-terrorism inquiry.

Sara Thornton says in a letter published in The Times today that the messages offering payments to those “with a raging credit card habit” have brought discredit on Thames Valley police.

The e-mails, which were sent to colleagues by a sergeant based at Milton Keynes, are unacceptable, Ms Thornton says, and she cannot defend the practice in any way.

“It brings discredit on Thames Valley Police and demonstrates an attitude to spending public money that has no place in the police service,” she writes.

Thames Valley Police said yesterday that Sergeant David Bald had been “spoken to and given advice” by senior officers.

Ms Thornton says that she has asked the force’s professional standards department to see if the incident was isolated or part of a wider problem.

She says that the force has worked hard to control the costs of Operation Overt, the investigation into an alleged terrorist plot to blow up transatlantic airlines in 2006, which became Britain’s biggest anti-terror operation. She discloses that to meet the demands of the investigation, 5,000 shifts were redeployed from local communities, and for these shifts officers received no extra payment.

The disclosure of the e-mails sent to officers across Thames Valley are deeply damaging to the reputation of the individual force and to the rest of the Police Service at a time when police budgets are under pressure.

Volunteers were told that night shifts, believed to be paid at £300 each, would give them time to “read a good book, take up botany or ornithology, study for your sergeant’s exams [or] work out the compound interest on a rest day’s pay”.

One message, marked “108 shopping days to Christmas”, sought officers for Saturday shifts and said that the payments “could buy the joy and admiration of your children on Christmas morning . . . is that not priceless?”

The internal e-mails were sent to officers across the force at the height of the search in King’s Wood and Fennels Wood, near High Wycombe, Buckinghamshire. Specialist teams searched the woodland while Thames Valley officers stood guard.

The force said that the e-mails were in poor taste and that its involvement in the operation cost the force £8 million, including £4.9 million in overtime.

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