A swan had its leg broken after a dog attacked it in Battersea Park, part of a growing trend of dog attacks on birds in Wandsworth, a charity said.

The cygnet, which suffered a broken leg and bite marks last Wednesday, was rescued by charity London Wildcare Trust (LWT).

A spokesman for the trust said: “We are seeing an increase in the number of incidents we are called out to.

"We are getting about 12 a month now, and those are only the calls we get called to, so it is a growing problem.

“We can’t say for sure if it is people doing it deliberately but it is a problem.”

Icy weather has led the swans and other birds to the edge of ponds, leaving them more prone to attack.

But notices in parks and around ponds warn dog owners to keep their pets away.

“It is actually an offence to let dogs run free near ponds,” the spokesman said. “But dogs on the loose will chase birds, not to kill it but only for a game.”

The increase in attacks are putting further strain on LWT, according to its founder Ted Burden.

The charity treats more than 4,000 sick and injured animals and birds every year.

Meanwhile, Scotland Yard is to launch a new police squad dedicated to tackling dangerous dogs being used in gang-related crime and antisocial behaviour.

New figures show that in eight months last year 494 dangerous dogs were seized by police in London compared with 43 in the four years leading up to March 2006.

There are 270 seized dogs in kennels awaiting court proceedings at a cost to the Met of more than £1 million a year.

The RSPCA recorded a five-fold increase in dog fighting between 2004 and 2006. A total of 137 fights involved 82 youths fighting their dogs in the park or the street.

A spokesman for the RSPCA said: “Our animal hospitals deal with the fallout from this problem on a daily basis, when they treat countless animals for bite wounds, stabbings, injuries from traffic accidents and diseases caused by indiscriminate breeding.”

• For information on LWT visit londonwildcare.org