Last July letters were sent to more than 250 estate agents warning that they could be fined if they put up 'for sale' signs or 'to let' boards unlawfully. The council has now secured its first prosecution and six more court cases are pending.

Estate agents can place boards on a building or land that is for sale, but signs erected on public land elsewhere need specific advertising consent. Ignoring the rules is an offence under the Town and Country Planning Act.

Some agents continue to ignore the legal requirement and erect signs on the sides of blocks, in communal gardens, car parks or on communal walls.

Last month Outlook Properties Limited in Stratford were fined £500 for breaking the rules by erecting a board in Manor Road, Stratford. The council asked for it to be removed but the board remained.

The council took action at Stratford Magistrates Court but the company failed to attend the hearing. In addition to the fine they were also made to pay £500 in court costs. The council was also granted a destruction order regarding the board.

Councillor June Leitch, executive member for crime and anti-social behaviour, said: "The council is currently investigating more than 100 cases of alleged unauthorised estate agent boards. They cannot say they weren't warned and we hope this successful prosecution will deter others from ignoring the legislation.

"We shall again be advising all estate agents of their responsibilities under the regulations. Most abide by the rules but some seem content to spoil the environment. It is not fair on those people who have to live amongst this clutter of signs."

The council will also consider seeking anti-social behaviour orders against persistent offenders.

If residents see what they believe is illegal or inappropriate use of estate agent boards they can contact the council's anti-social behaviour hotline on 0800 731 3300.