Twelve men were questioned after the operation on Monday, which was the culmination of a three-year RSPCA investigation.

Addresses and outbuildings were searched in Oxford, Barnsley, Birmingham, Chesterfield, Gainsborough, Huddersfield, Leicester, Liverpool, London and Scunthorpe.

An RSPCA spokeswoman told BBC News Online that some of the men questioned by its officers were later arrested by police.

They are expected to be quizzed again at a later date.

'Barbaric' sport

Chief Inspector Mike Butcher, from the organisation's special operations unit, said: "We are extremely pleased with the operation and hope to make more arrests shortly.

He added: "It's astonishing to think that, even in the 21st century, there are still a small minority of people who enjoy the barbaric sport of pitting one dog against another and we will continue to make sure that those involved are dealt with through the courts."

A total of 73 dogs and a number of items including treadmills, scales, veterinary kits and breaking sticks were recovered during "Operation Gazpacho".

Blood and hair samples were also taken away for DNA analysis.