The start of Britain’s grouse shooting season has been overshadowed by wildlife protection protests, marking the growing confidence of animal rights supporters that they are about to make their biggest breakthrough since the hunting ban in 2004.

As the countryside echoed to the sound of gunfire on the Glorious Twelfth, opponents took part in a protest ramble on Ilkley Moor, the site of the only shoot still taking place on public land. In central London, thousands of marchers were told by speakers including the BBC presenter Chris Packham that the days of the West Yorkshire shoot were numbered, with Bradford council under unprecedented pressure not to renew the lease next year.

“I think that when people now see others killing for the psychopathic joy of it they are increasingly sickened and the reason for that is that our wildlife is running out,” Packham said. He told the Observer that public support for conservation in the UK had risen on the back of global outrage after Cecil the lion was killed in Zimbabwe in 2015. Social media is another factor.

“The RSPB published video of marsh harriers being killed on a grouse moor in Yorkshire and within hours of that material going on to YouTube it has been spread all around. Everyone is instantaneously angered as it gets shared and there is frankly nowhere for these criminals to hide,” Packham said.

The marchers, wearing fox head masks and carrying banners condemning the badger cull, made their way to Downing Street after speakers said that loopholes continued to allow hunting to go on. Danielle Flynn, 55, a former hunt saboteur from Glasgow, marched with her daughter Karen, who said social media had played a big part in the resurgence of interest in animal rights. “A lot of them might be apathetic about politics but they might, for example, take an interest when I talk to them about animal testing and makeup,” said the 24-year-old.

Jordan Psaros, 26, from Braintree in Essex, said: “I’ve always been an animal lover but I basically became involved in this after I saw videos online of foxes being killed by dogs set on them by hunters on horseback. A lot of people of my age are waking up to what is going on.”

Animal rights groups have been emboldened by the public reaction to recent controversies. Arsenal football club owner Stan Kroenke was forced to order his new TV streaming service to stop showing big-game hunting and Vinnie Jones was caught up in a row over a photograph of 100 dead foxes that appeared on his Twitter feed.

Hunting also featured in the general election after Theresa May declared her support for a free vote on overturning the ban, with some Tories complaining afterwards that this contributed to “toxifying” the party brand. Focus group Britain Thinks also found that while the so-called “dementia tax” was key among older voters, the prospect of a foxhunting revival alienated many swing voters.

Pro-hunting advocates argue that it is impossible to say whether the animal rights movement is resurgent in terms of actual numbers, arguing that hard data suggests the public do not change their vote on the basis of hunting or shooting issues. A YouGov poll in May put support for the ban at 67%, which suggests a decline in support, they said.

“If there has been any genuine resurgence of animal rights activism, it can almost certainly be attributed to social media,” said Liam Stokes, head of shooting at the Countryside Alliance. “Animal rights messages are very simplistic, and simplistic messages spread well on Twitter and Facebook, particularly when broadcast by celebrities like Packham and Brian May. The arguments for wildlife management are complex, nuanced and sometimes paradoxical, and don’t lend themselves so easily to social media.”

Shooting continues to be big money. Yesterday saw the Gleneagles Glorious Grouse Race, in which shooters race to deliver the first grouse of the season to the town and onwards to London. Grouse killed by shooters including the Olympian Peter Wilson were due to be helicoptered down to be served at London’s Harwood Arms gastropub.

“All the evidence is there that it should be stopped and there is a lot of support for that locally,” said Luke Steele of Ban Bloodsports on Ilkley Moor, who said that backing was coming from the local conservation group and a new Labour MP who recently took the seat from the Tories.

“We have seen that notable breeding bird species have gone extinct or declined by more than half, for example. Then there is the environmental damage caused by sections of the moor being set alight, and there are walkers who are fearful of the guns.”

But Edward Bromet of the Bingley Moor Partnership, which runs the shoot, insisted that grouse shooting aided the moor’s upkeep and described those organising yesterday’s protest as an “extreme” group.

“The key point here is that what the partnership agreed to do 10 years ago, when Bradford offered the moor on a lease, was to restore the moorland. We have done that primarily at our own cost, to reduce the bracken, which the people of Ilkley were very frustrated by, and restore the vegetation.

The Countryside Alliance has also turned its fire on Packham, sending a letter this weekend to the BBC arguing that it was unsustainable for him to be allowed an “unchallenged platform” on programmes such as Springwatch while he aligned himself with “the most aggressive elements of the anti-shooting campaign”.

Packham said: “There is no conflict. I have a working relationship with the BBC. We have an agreed protocol and I have not deviated from it. The Countryside Alliance are upset because they are on the back foot. We are winning and they are lashing out.”