More foxes are being killed and more people are hunting with hounds than before the hunting ban, Countryside Alliance chairman Kate Hoey has said.
Hounds are still killing foxes, Ms Hoey says
The law was broken, inadvertently, as dogs continued to kill foxes, said the Labour MP for Vauxhall.
Meanwhile the League Against Cruel Sports said it had sent to police dossiers on 33 hunts suspected of most frequently breaking the year-old ban.
The group said it feared a growing number of hunts were flouting the law.
Hunting foxes with dogs was made illegal in England and Wales under the Hunting Act last February, but hounds can be used to follow a scent and to flush out a fox.
The fox can then be killed by a bird of prey or shot - if only two dogs are involved.
But Ms Hoey told The Daily Telegraph: "Accidents happen. If you're going out legally following a scented fox trail and the hounds come across a real fox, they can kill it before it is possible to shoot it."
HUNTING ACT 2004
It is an offence to hunt a wild mammal with a dog
Some forms of hunting are exempt including:
Using no more than two dogs to flush out a mammal to be shot
Flushing a mammal from cover in connection with falconry
It is a defence to believe that the hunting was exempt
She said that she was not aware of the Crown Prosecution Service having prosecuted anyone for breaching the ban.
"You have to prove that the person who is in charge of the hounds has actually gone out with the intention of hunting illegally," Ms Hoey said.
She said the ban, which took 700 hours of parliamentary debating time, was inconsistent and hard to enforce.
A spokesman for the Countryside Alliance said anecdotal evidence suggested that the number of foxes killed by hunts and farmers had gone up since the ban took effect.
"All the hunts have got far more people going out with them," Ms Hoey said.
"It's part of the British rebellious streak that as soon as something is banned it becomes more attractive."
She admitted that some of her own worst fears had not been realised since the ban took effect.
Ms Hoey says the Hunting Act is inconsistent
"No hounds have been put down, nobody has lost their job," she said. "A year ago everybody was so depressed, then people realised they could just carry on."
A spokesman for the League Against Cruel Sports said it was difficult to believe Ms Hoey's claim that hounds were killing foxes by "accident."
The group also said it has sent dossiers to police forces around the country on the 33 hunts with the highest number of credible allegations of illegal hunting against them.
The allegations were based on reports from the group's "Hunt Crimewatch" volunteers, calls by members of the public and stories in the media.
"We are delighted that many hunts have changed their practices in order to obey the law," League Against Cruel Sports chief executive Douglas Batchelor said.
"Unfortunately there are extremists who believe they are above the law. They must be investigated and, where the evidence is clear, prosecuted."
The organisation has brought one private prosecution for allegedly defying the ban.
Huntsman Tony Wright denies breaking the ban in Devon and a court hearing is expected in March.