Residents who buy anything over £35 from a company calling unannouced has a seven days 'cooling off' period to change their mind.

It is a criminal offence not to give notice of these cancellation rights and can render the contract unenforceable.

Councilor Carole Kavanagh, executive member for Environmental Protection, said: "The Trading Standards Section are receiving an increasing number of complaints about people, who turn up unannounced on the doorstep offering to do work.

"They often prey on the elderly using aggressive and intimidating tactics to con them into having work done which they neither want nor need, and though the cost usually starts low it soon spirals as these rogues 'find' more work to be done.

"If things go wrong, it is very difficult taking action against this sort of trader as they don't have fixed trading addresses and although their victims have civil rights, the workmen usually vanish once they have the money making it impossible to take any action against them."

A trading standards spokesman said: "Generally, if you do agree to buy something from a company who cold calls you at home, costing more than £35, then you have seven days to change your mind and cancel the contract - your 'cooling off' period. Failure to give Notice of Cancellation Rights constitutes a criminal offence and may mean the contract is unenforceable against you.

"The advice from Trading Standards and the Police is not to buy anything or agree to have work done on your home by any trader who cold calls even if they telephone you first. Always wait until you have been able to get other quotes from established traders to ensure you get the best deal.

"If you want further advice about your rights against this type of caller, where you have agreed to have some work done and want to cancel, or have been called on by unannounced workmen offering gardening, driveway repairs, fascia or guttering work, or general building or repair work please contact Consumer Direct on 08454 040506."