Pressure is mounting on the Government to amend the ban on hunting after one of the Act's architects appeared to admit it simply was not working.

Hunt campaigners have seized upon the comments of John McDonnell, a high profile anti-hunt Labour MP, who said of the 2005 Hunting Act: "It took a long time. There was a lot of discussion. We thought we got it right, but we clearly haven't in this instance."

The Countryside Alliance, which is stepping up its campaign for the hugely controversial law to be repealed, compared Mr McDonnell's comments and the stirrings of pressure for an amendment to toughen up the ban to an unsatisfied architect of the pyramids.

"They now want the Act amended," said CA chief executive Simon Hart, "which in parliamentary terms is rather like the Pharaohs viewing the finished pyramids and deciding they would prefer them square."

Mr McDonnell made the comments during an interview on Radio 4. He was instrumental in getting the Hunting Bill through Parliament.

The MP for Hayes and Harlington in Middlesex, who is also chairman of the Socialist Campaign Group of MPs, has not embellished on the bombshell comments since.

The CA claimed last night the anti-hunt movement was split between those who believe greater enforcement is the answer to curtailing the alleged illegal hunting, and those who believe an amendment to strengthen the hunt law itself is required.

After the opening weekend of meets earlier this month, one leading Somerset hunt monitor, Helen Weeks, said so many hunts were routinely breaking the law that an amendment was required.

At present, all prosecutions of hunts, including both 'state' prosecutions led by the Crown Prosecution Service, and the private ones led by the League Against Cruel Sports, have been frozen, pending the outcome of the Tony Wright appeal case.

That three-year-old case – the first ever prosecution of a huntsman – is the subject of a verdict which will set a precedent for the way the law is dealt with in court.

Appeal court judges will have to decide on the thorny issue of intent – is it down to the prosecutors to prove a huntsman intended to break the law, or is it for the huntsman to prove that they weren't?

Until that is decided, no prosecutions can continue, and should that decision go against the CPS and the League, then the future of all West prosecutions – including that against the Devon and Somerset Staghounds – will be thrown into doubt, along with the future of the law itself.

The International Fund for Animal Welfare, which funds many monitors in the West, said more police were needed out in the fields, along with more monitoring. For IFAW, the intimidation and violence against its monitors is a big signal that hunts are still breaking the law.

"Since this cruel sport has been outlawed, IFAW hunt monitors have peacefully filmed hunts and passed on evidence of suspected law-breaking to the police," a spokesman for IFAW said.

"Disturbingly, every year monitors are assaulted and intimidated by hunters and their supporters, who don't want their activities to be filmed.

"IFAW will not be intimidated and our monitors have pledged to continue their difficult jobs, but we have to see more police forces also monitoring hunts," he said, adding that anti-hunt supporters should write to their MPs to demand the law is properly enforced.

But the Countryside Alliance said the growing debate about whether the law itself is working is greater proof a repeal is needed. "Mr McDonnell's comments highlight a widening schism within the anti-hunting movement," claimed Simon Hart, the CA's chief executive.

"The League Against Cruel Sports continues to argue that the Act is clear and enforceable, whilst Mr McDonnell and other organisations are now admitting it is a bad law.

"It is in the interests of animal welfare, the economy, the police, field sportsmen of every kind, Parliament and the wider community to rectify the situation, sooner, not later.

"There is only one answer to the Hunting Act and that is repeal," he added.