Cowboy roofers are targeting elderly householders and persuading them to pay thousands of pounds for work which is either unnecessary or sub-standard, West Yorkshire Trading Standards has warned.

Officers say glossy leaflets are being delivered door-to-door promising new uPVC fascia, soffits and guttering for just a few hundred pounds, all backed by an impressive-sounding 10-year guarantee and trade names similar to well-known national home improvement companies.

However, recent complaints across West Yorkshire have indicated that householders who take up these offers are then told their roofs need urgent and extensive work to replace rotten felting and wooden battens.

The work is quoted at thousands of pounds and the trader states they want to start immediately.

Faced with these tactics, many householders are said to be agreeing to the work without a second opinion.

Councillor Val Slater, chairman of the West Yorkshire Trading Standards Committee, said any consumers who suspected rogue traders were working or leafleting in their street should report it to the Citizens Advice Consumer Helpline on 03454 040506.

"Rogue traders cause misery to their victims, who are left seriously out of pocket by a combination of shoddy and unnecessary work, and much of this type of crime goes unreported," she added.

David Lodge, head of Trading Standards, said: "My advice to homeowners wanting to invest substantial sums in home improvements is to choose roofers very carefully.

"They should also insist on written contracts detailing works to be carried out.

"This service can and will take action against the minority of traders who engage in unfair commercial practices."