Animal rights campaigners have accused a hunt supported by David Cameron of being part of a "nationwide criminal conspiracy" to sustain fox populations for hunting.
An investigation by the League Against Cruel Sports (LACS) found that artificial earths – structures built to provide breeding places and homes for foxes – are being maintained in areas used by all but three of the 24 hunts that it monitored around the country.
Campaigners argue that a ban on the hunting of foxes with dogs introduced in 2004 made artificial earths "pointless", and that that their upkeep "points to a nationwide criminal conspiracy by fox hunts to encourage and sustain fox populations in order that they can be hunted".
"From building extensive earths, to providing food, water and bedding, the very notion of hunts following artificial trails becomes ever more laughable," said Professor John Cooper QC, chairman of the LACS.
"Whilst most of us suspected the hunts would carry on their nefarious activity, I for one never quite imagined they would be as blatant and, frankly as stupid, as to continue their use of artificial fox earths." Between June and October this year, investigators from the LACS visited 16 counties in England to inspect land used by 24 hunts. Artificial earths with signs of recent renovation or food supply were found at 21 of them, according to the report.
The LACS claimed to have found six artificial earths on land regularly hunted by the Heythrop Hunt in Gloucestershire, the local hunt in David Cameron's Witney constituency and one that he has ridden with on at least six occasions. Video footage obtained from hidden cameras also showed a man dumping offal near an artificial earth in Dorset and remains of broiler chickens were found near one of the structures on land regularly hunted by the Heythrop Hunt.
While the LACS acknowledged that it could provide no direct evidence that the named hunts were complicit with the building and maintenance of the artificial earths, it said: "It is clear that someone has been maintaining the earths on the country of these 21 hunts, and one must question whether or not this can be pure coincidence."
Tim Bonner, a spokesman for the Masters of Foxhounds Association, denied that the artificial earths had anything to do with the hunts named in the report.
"The earths are not only used by hunts. They are also used by gamekeepers to locate foxes so they can find them and kill them," he said. "Most of the hunts I called didn't know the earths were there," he said.
Mr Bonner said that most hunts still killed foxes as part of a "service" to landowners, but shot them "legally". "I think there is a dispute over what the law means. The League Against Cruel Sports has attempted to suggest that the legislation means that hunts can't use any form of hunting as a fox control method. That is clearly wrong. The legislation has a series of exemptions."
But Professor Cooper said: "We have never heard of gamekeepers using artificial earths to decrease numbers. Our research shows that they are only ever used to increase numbers. That begs the question: why should numbers be increased? We answer: to be hunted."