About 50 competitors watched in astonishment as frogmen emerged from the water and emptied keep nets. Other demonstrators, some in small boats, blew hunting horns, beat dustbin lids under water and dragged ropes across the river to create waves.
The event, which was filmed for a new series of the Channel 4 access programme Free For All, drew angry complaints from club members that they had been 'set up' for the cameras. Peter Gilbert, chairman of the club, said later that a large pile of litter collected by the saboteurs and photographed by the London film company, Filmit Productions, had not been deposited by his members.
Davey Shephard, spokesman for the Bristol-based CAA, warned yesterday that the incident marked the beginning of a national campaign against anglers. Mr Shephard said that although the group had only 200 members it could call on support from thousands of hunt saboteurs. He said: 'Two of our supporters were assaulted after the cameras had left the Isis club match. One was pushed in the river, another was hit on the nose. It's possible their violence will increase but it wouldn't put us off sabotaging anglers. We want angling banned.
'Three reports since 1980, two of them by the University of Utrecht, say fish are capable of feeling fear and pain. Anglers say they just want to enjoy the countryside. We say they don't have to abuse fish to do that.'
The CAA says it has produced a video for schools called Angling: the Neglected Blood Sport, which features a live eel having its head chopped off.
Its newsletter, Pisces, draws attention to 'the bright side of the recession' - the bankruptcy of tackle shops.
Isis club members reacted angrily to the disruption of their match and the presence of cameras. 'It was a total set-up,' Mick Lansdown, 37, said. 'They showed up with this litter but I can take you down there now and it's one of the cleanest pieces of river in the country. And it's rubbish about the violence. Considering they were going round with sticks tapping people's fishing rods they'd paid pounds 150 for, I think the anglers behaved very well.'
Filmit's executive producer, John Sampson, declined to comment, but a Channel 4 spokesman yesterday denied allegations that the club had been targeted for the film. He said: 'CAA sent in a proposal that said there would be a disruption of this match on 17 January so it was clear that the demonstration had been planned and was going to take place anyway.'
Davey Shephard said: 'We wrote to Filmit and asked if they'd be interested in our issue. They asked us to outline what we'd do and we sent back a synopsis. If all you suggest to them is sitting in front of a camera talking, that probably hits the bin. At that point it was decided that the direction of the programme should be sabotaging a match rather than talking about it. There was a good chance it would have been sabotaged anyway but to be honest it was selected specifically for the film.
'The company came down a few days beforehand to check the venue, to make sure it was film-worthy and during that time we talked about what we wanted to get over on film.'
Peter Gilbert, the club chairman, said yesterday: 'I've heard of isolated incidents involving a few agitators at matches but in 20 years of angling there's been nothing on this scale. So far as I know this was the first and largest demonstration of its type in the country, a very big effort because the TV cameras were there.'
'I told my members afterwards that angling won a great victory on this day because members weren't provoked into violence. Having said that this sort of thing will have to be dealt with. You can't just sit around and let them get away with it because obviously the police aren't going to do anything.
'I'm totally non-violent but in future anglers will have to organise a group which would have the right to eject saboteurs with a minimum of force. This would be the right way to nip it in the bud.'