A yob leapt on a volunteer caretaker and tried to throttle him after being asked to leave a private garden in one of London's most exclusive neighbourhoods.

The man, who was locking up St James's Square - a garden off Pall Mall surrounded by Georgian mansions and private members' clubs - was attacked after asking a visitor to leave the garden, which shuts at 4.30pm.

As a result, the gates to the square, normally open to the public during office hours, have been locked since Friday's incident.

Deputy chairman of the St James's Square Trust Carol Hannay told the Standard the worker had been left "very upset" by the attack.

Ms Hannay said it was "very sad" to have to shut the garden, but added: "We can't put lives at risk, or health at risk."

The assault happened as a new volunteer attempted to clear the square before closing it up for the weekend.

"Someone took exception to being asked to leave at 4.30," said Ms Hannay. "The guy locking up walked away towards the gate - then he was jumped on from behind.

"My understanding is he was grabbed around the neck. It was quite nasty. It wasn't something you could brush off."

The square, funded by leaseholders of the offices and clubs surrounding it, is used by workers and passers-by during the week.

Ms Hannay said antisocial behaviour had become an increasing problem in the last year - as a result of which the regular garden keeper had resigned.

"It's not just junkies and winos," she said. "It's a variety of people - there are office workers and people in suits. There's people that are have either been drinking or taking drugs, but there's plenty of people who should know better.

"It's sad - it's a real oasis and we've put a lot of effort into improving the garden over the last four or five years.

"The only thing we can do is close it for the moment while we look at our options."

Ms Hannay added the trust is appealing for donations to buy a set of new railings that would keep the garden more secure. Anyone interested in helping is asked to e-mail trustees@stjamessquaretrust.co.uk.