This image often accompanies the "strawberry meth" warning

The warning said that the drug was being given to children outside their school gates.

At least 80 schools in west Oxfordshire received an e-mail warning, leading to some holding special assemblies.

Thames Valley Police said the error was down to an officer new in his post who had received an e-mail internally and had acted in good faith.

The force sent out a retraction after discovering it had been the victim of a hoax, and said no such incidents had taken place.

The officer should have double checked

Ch Insp Dennis Evernden

Ch Insp Dennis Evernden, of Thames Valley Police, said: "We would like to apologise for any unnecessary concern that we may have caused to schools or parents by sending this warning out about a drug that proved to be a hoax.

"One of our officers, who is new to his post, received the e-mail internally in good faith and forwarded it on to the schools in West Oxfordshire to warn them.

"But after checking its veracity, it was found to be a hoax and a retraction was issued the next day.

"The officer should have double checked before taking this action, which he did take with the best intentions, and we will be making sure this sort of thing does not happen again."

Last year, the charity DrugScope said it believed the hoax e-mail originated in the United States.

It said there was no evidence to suggest that crystal meth - an illegal drug - flavoured with strawberries was circulating in the UK.

A Thames Valley Police spokeswoman said the force would not be holding an internal inquiry over the incident but, instead, it would be reminding its staff of necessary procedures.