Police have also started an informers' website

Cambridgeshire Police has come up with the novel scheme as part of a crackdown on persistent offenders called Operation Target.

Officers have drawn up a list of the 500 most prolific criminals and are sending out timely reminders to those who are celebrating their birthdays during the 12 weeks of the operation.

The greetings card list runs to more than 110 during that time.

The number of arrests we make is increasing on a daily basis and the people of Cambridgeshire can be assured we are working around the clock to get these criminals off our streets Superintendent Paul Phillipson

The card shows a picture of a birthday cake on the front with Happy Birthday written underneath. Inside it has the Operation Target logo on one side and the force crest and 'from all of us' on the other.

Superintendent Paul Phillipson, who is heading Operation Target, said: "This is the first time we have used this tactic in the county. We hope that it will make them stop and think about their actions.

"The card is a simple reminder that we are around and we will be keeping a close eye on people who repeatedly offend.

"We are not prepared to tolerate the misery and impact these people have on the communities of Cambridgeshire. We intend to make life very difficult for them.

'Drop on their doormats'

"The number of arrests we make is increasing on a daily basis and the people of Cambridgeshire can be assured we are working around the clock to get these criminals off our streets.

"The birthday cards have a long shelf life so they will be used initially during the Operation Target campaign, but criminals who celebrate their birthdays after the 12-week period can also expect one to drop on their doormats."

Operation Target high profile is aimed at cutting burglary, drug dealing, car crime and street robbery.