The pro-hunting Countryside Alliance said up to 100 foxes died as hundreds of thousands of hunters and spectators took part in more than 300 hunts on the opening of the first season since the practice was legally banned.
Anti-hunt protesters, many armed with cameras, monitored the day's events, watched by up to 3,000 police officers.
Hunt leaders were determined to test the legislation to the limit and more than 50 hunts used birds of prey to hunt down foxes.
Thirty-six riders and 31 hounds rode out with the historic Cheshire Forest Hunt and there, in an attempt to bypass the hunting ban, an eight-month-old Harris hawk, called Alice, was present.
Peter Heaton, joint master of the Cheshire, said: "Part of the exemptions is that you can use an unlimited number of hounds to flush for an unspecified mammal, and the process could include using a bird of prey. The hounds are not hunting, but they are flushing for the hawk to hunt. It's one of the ways we are testing the legislation."
Dr Jane Evans, who was monitoring the Cheshire, complained she was intimidated and insulted for much of the day. The hunt, she said, rode out with a full pack of hounds.
At Tony Blair's local hunt, several hundred spectators turned up at Sedgefield's Dun Cow Inn to see in the new season. Mark Shotton, the master of the hunt, also brought in a bird of prey to get around the new rules, this time a gigantic eagle owl.
Mr Shotton, 65, said: "We hunted within the law; I don't believe we had any choice in that. We must keep this hunt going, not least for the sake of tradition but also the many jobs that rely on trade from the 100-plus people that ride out with us."
The incidents infuriated hunt saboteurs across the country, with the League Against Cruel Sports claiming to have evidence of breaches of the ban. Mike Hobday, a spokesman for the organisation, said it had received reports of illegal hunting taking place yesterday. One hunt in Surrey, he said, had been caught on video chasing down a fox. The evidence was being passed to police.
"The tape shows the fox clearly being chased by hounds, and the riders going along, making no effort to stop them. It is a very clear chase of a fox," he said.
In Gloucestershire, at first glance, the first weekend of hunting by the "distinguished" Beaufort Hunt on the Badminton estate looked no different to any other year.
But, despite expressions of determination to soldier on from hunt leaders, hunting has changed. The scent did not lead to a fox. Instead, an " organic-based smell" had been laid along pre-arranged tracks. There was no quarry for the hounds.
At least, that was the plan. "Accidents happen," admitted Nigel Maidment, secretary of the hunt. "A fox can jump up - this is where they live, after all." Hunt officials claimed no fox was killed, although one young woman on horseback suggested otherwise. As the hunt passed a group of supporters, someone asked how it was going. She smiled and slashed her finger across her neck, indicating a death - of what, she did not say. Another woman on horseback added: "We shoot them now, you know. "
Ian Farquhar, joint master of the Beaufort, is hoping that in government under a new leader, the Conservatives would repeal the legislation. But the Tories, too, are divided.
Ann Widdecombe, Conservative MP for Maidstone and The Weald, criticised police forces for allowing the hunts to ride out for the new season despite the sport being banned.
"We passed a very generously spirited law," she said. "But the law is being flouted because it is either unworkable or the law enforcement agencies lack the will to make it workable."
Additional reporting by Jonathan Thompson
The Hunting Act 2004 makes hunting with dogs an offence in England and Wales.
The ban covers the hunting with dogs of all wild mammals, including fox, deer, hare and mink.
It is still legal to use dogs to hunt rabbits or rats, but there are strict limits to prevent fox-hunters going out with hounds claiming they are looking for rabbits.
It also makes it an offence for a person to allow their land or dogs to be used.
Police are given powers to arrest anybody they suspect to have committed these offences.
A person found guilty of an offence is liable to a fine of up to £5,000.
100 Foxes feared killed by hunts in England and Wales yesterday
£6,000 for one golden eagle; some of the birds were used in hunts in Co Durham
300,000 people taking part in, or supporting, hunts yesterday, said the Countryside Alliance
£5 for a pack of 10 Christmas cards featuring the Dunston Harriers hunt
2 dogs allowed to flush a fox to a waiting gun
3,000 police officers estimated on duty at hunts yesterday
20 new members yesterday at the Bilsdale Hunt, North Yorkshire
£30 cost oF family membership of the League Against Cruel Sports
157 breaches of legislation alleged by hunt saboteurs against hunts up to yesterday