Animal activists called on hunters to learn to live with the rules and condemned the nation-wide rallies, involving almost 270 hunts, as an offensive publicity campaign.
"The response of the rural community to the (Hunting) Act, whatever its status, is evident by what is hapening here today, and is being mirrored across the whole country by something like a half million people," said John Jackson, head of the pro-hunting Countryside Alliance, at a hunt in central England.
"This whole saga is developing into a crisis of confidence - confidence in our government, confidence in our national institutions and confidence in our constitution," Jackson told a rally in a field in the picturesque village of Stratton Audley, home of the centuries-old Bicester with Whaddon Chase Hunt.
"I am certain that this crisis will be recognised, will be addressed and that common sense will prevail," he said, pledging that Prime Minister Tony Blair's government, which pushed through the legislation last November, would feel the fallout at general elections expected in a few months times.
Up to 1,000 hunt enthusiasts, young and old, some on horseback, flocked to the village to defend a sport that has been a part of British country life for centuries.
"I love hunting, it is such good fun to ride through the countryside," said eight-year-old Harriet Mainds, who has already been hunting for three years.
Pledging to keep within the new law for now, riders at some hunts killed foxes in two-dog forays that are still legal. Others chased after fox scents only or galloped through fields in mock hunts.
At the Bicester hunt, actor Jeremy Irons who starred in "The French Lieutenant's Woman" and "The Mission", was among a group of pro-hunting celebrities who turned up, saying he opposed the fact that the government was suppressing minority rights.
"I am turning up to show support and to show the great hope we have that this legislation will be overturned either for legal reasons or because we vote in politicians who understand that it is not the government's job to tell people how to spend their time, how to live," he told AFP.
The actor, who has hunted since he was 13 but was on foot Saturday because his horses are in Ireland, did not expect the day's protests would change the law quickly.
The hunting lobby also contends the ban could place at risk thousands of jobs they say now rely on the sport, but animal activists remain adamant, describing hunts as cruel and inhumane.
Saturday "is a media event set up by the hunters who will turn out in force to demonstrate that they are invincible," said Pennie Little, a vocal campaigner for animal rights.
Many questions remain about how the law, which follows a similar hunting ban that took effect in Scotland in 2002, will work in practice, with the police admitting that it could prove difficult if not impossible to enforce.
The ban most notably affects fox hunting - a centuries-old tradition in which riders on horseback gallop after foxhounds who trail a fox and, if they are successful, will catch it, kill it and rip it apart.
Lesser known, but also to be prohibited, is hare coursing, a spectator sport in which a pair of greyhounds are set loose after a hare which often, but not always, gets away.