THE taxman will be mingling with the crowds at Wimbledon this year in search of homeowners who rent out their properties for thousands of pounds but fail to declare the earnings.

A leading firm of accountants estimates that Revenue and Customs could net more than £500,000 from families who give up their houses to players and tennis fans for the duration of the championships.

Geraint Jones, a tax adviser at Blick Rothenberg, said: "Every year many Wimbledon residents jump on the tennis bandwagon to make some extra cash. It ranges from renting a room, a parking space, selling strawberries and cream, allowing souvenir sellers a pitch in the front garden, to moving out for the two-week tournament and renting out the house.

“This year Wimbledon properties are being rented from £900 a week for a one-bedroomed apartment to £6,000 a week for a five-bedroomed house. This all has to be declared to the Revenue.”

As well as patrolling the streets in search of rented properties and stalls on front lawns, tax teams will be monitoring local and national newspapers. Specialist agents are required to supply the Revenue with a list of properties on their books.

Joanna Doniger runs Tennis London, a short-term rental company that houses people during the championships. Her company organises about 150 rentals each year. “I know the Revenue keeps a close eye on this market,” she said.

“In the past I have been asked to provide invoices detailing the rentals after the owners of the properties have lost them.”

Karen and David Champion live a little more than 300 yards from the Wimbledon grounds and can see the courts from their bedroom. They will spend the two weeks in Spain.

For a weekly rent of £1,400, the Champions will this year be leaving their three-bedroomed house to an Australian family. In the past, players have rented it, including the Russian-born Svetlana Kuznetsova.

Mrs Champion, 29, an investment banker, said: “Svetlana left our house in a bit of state; but Tennis London cleaned it and had everything ship-shape within three hours.”

Although the Champions store a few personal possessions in the garage when they are away, most of their belongings are not packed. “People want to stay in a house when they are at Wimbledon,” Mrs Champion said. “So we are asked not to put things away.”

Failure to declare earnings from Wimbledon can result in a fine and demands for back tax. Although the first £4,250 is free from tax, any excess attracts a liability of 40 per cent for higher-rate taxpayers.

Smaller amounts, such as money from renting out a car parking space in front of the house, are not taxable but residents must still declare them.

The Revenue confirmed that tax officials in Wimbledon will be vigilant. A spokeswoman said: “It’s the job of our investigations team to know what is going on in the area. People are well aware when their income will be taxable — there is no excuse for that income not to be declared. Our advice is, don’t wait for us to come looking for you.”

Another concern for the Revenue and trading standards officers are traders who sell food, drink and counterfeit souvenirs such as T-shirts and posters from temporary stalls. This year Wimbledon has been declared a trademark and stallholders have been notified. Wandsworth Borough Council said that officers from its technical services department carry out regular inspections.

A council spokeswoman said: “Where a stallholder has been identified as selling counterfeit goods, we would explain the breach and issue a warning. If the trader ignores the warning we will seize the goods.”

There is one small consolation for those operating within the tax law. Mr Jones said: “People can make use of the rent-a-room allowance. If they are operating a business such as Henmania memorabilia, they should ensure that all expenses such as tools or electricity or raw materials are claimed.”