You can't mention this to anyone because, obviously, what I'm doing is illegal

Trainer Lennie Knell

Each year �1.5bn is gambled on the dogs in the UK.

However, according to one of the most experienced kennel hands in the sport, a huge number of races are fixed, particularly those run on non-official tracks.

Over-feeding dogs

On camera, the kennel hand admits to fixing hundreds of races, and claims the public has more chance of winning the lottery than making money at the dogs.

Trainer Lennie Knell and colleague Colin West are caught on secret camera offering to fix a race by over-feeding a dog at a race track in Catford, south London.

Paul Kenyon and dog

At one point Mr West boasts they made �11,000 from a fixed race.

Trainer Mr Knell warned the BBC undercover team: "You can't mention this to anyone because, obviously, what I'm doing is illegal."

At a track in northern England a well known greyhound drug dealer sold the Kenyon Confronts team various drugs to speed up, and slow down, dogs.

The dealer said the strongest drug he uses is cocaine and claims to have made �29,000 in one day on fixed races.

Mass grave

A greyhound's skull

The programme also discovered a mass grave for dogs in Oxfordshire.

An estimated 10,000 greyhounds retire from racing each year but only a small number are re-homed, as many disappear in mysterious circumstances.

Trainer Steve Davis keeps hundreds of dogs at his kennels in Oxfordshire and, according to former workers, has shot dozens with an unlicensed sawn-off rifle.

They said Davis saw greyhounds as a commodity and killed them once they were too old or injured to race.

In a late night raid the Kenyon Confronts team dug up some of Davis' land and found the mass grave hiding the carcass of one dead greyhound and the bones of others.