Four suspected conmen working as gardeners were arrested in sting operations in Oxford and Witney by trading standards officers and police.

The crackdown is estimated to have denied the traders a total of £11,500.

Details of the intelligence-led operations, released last night were minimal because criminal charges could be brought, but the crackdown started in Headington on Wednesday morning.

A young couple was targeted by a gang from Dunstable, Bedfordshire, who had attempted to charge them £3,500 for what trading standards officer Martin Woodley described as "appalling work".

Three men fled when the authorities turned up, but one was detained.

The following day two men were arrested after cold-calling at an elderly couple's home in Oxford, where further "serious offences" were committed.

At the same time, in a separate incident, two men were arrested in Witney after police acted on an anonymous tip-off that gardeners tried to charge an elderly lady £3,000 for substandard work.

Last night, trading standards officers said those arrested could be prosecuted under consumer protection and fraud legislation.

Mr Woodley said: "A lot of people will become repeat victims because these rogue traders know what they can get away with. They target the vulnerable.

"People should be on their guard - never say yes for work, make sure workmen have proper paperwork on them and never let them inside your house. Very few reputable businesses knock on the door touting for trade."

Yesterday, four men were stopped by police as they returned to a woman's home in Witney to collect £500 for work carried out at an earlier date.

Experts said rogue workmen targeted households at this time of year to do gardening work. In the autumn, conmen tended to prey on vulnerable people by offering to carry out roofing work.

Nigel Strick, head of Oxfordshire trading standards, said: "There appears to be a team of rogue traders operating in the county, offering to do gardening work.

"We would strongly advise all residents not to deal with traders who call at their house.

"If you need gardening work done, ask your friends and neighbours to recommend a traders and get a couple of quotes to make sure you are paying a fair price.

Staying safe

Do not agree for work to be carried out by firms that call without an appointment.

Never say yes to work immediately

Always demand to see identification from workmen

Always demand quotes for work written on official, headed paper

Be prepared to shop around for several quotes

Never let workmen into your home

If you need gardening work to be carried out ask your friends, family or neighbours to do it