The 83-year-old lady received a visit from a man claiming to be from the gas board but after the quick-witted woman asked for his password, he fled, leading officers to believe he was probably bogus and the lady had avoided becoming a potential crime victim.

Insp. Jes Holland from Burnley Police said: "We believe a number of bogus officials are currently in operation in Burnley with several elderly people already having fallen prey to their callous crimes.

"Patrols have now been stepped up in these areas and letters urging witnesses to come forward are being distributed."

He added: "Unfortunately these callous criminals tend to target the elderly and most vulnerable but there are a number of things residents can do to protect themselves and this lady provides us with a shining example. I would like to commend her foresight and thank her family for advising us of potential criminal activity in her home area which is now being investigated."

Insp. Holland advised the following to anyone who receives an unannounced caller at the door, particularly anyone purporting to be from the gas, water or electricity board:

• Before you answer the door, stop and think if you are expecting anyone. Ensure your rear doors and any other doors leading outside are locked before you approach the front door.

• Open the door with the chain or door bar in place or talk through a window instead.

• Aways ask for ID. Genuine callers will have identification. Phone the person's organisation and confirm their identity. Genuine callers will be happy to wait.

• Some utility companies operate a password system. Choose a password only you will know and if an official arrives, ask for the password. If they can't recite it. Don't let them in.

Finally, he urged, if you are still unsure, do not let the caller in, dial 999 and ask for the police.