Michael Yardley, national spokesman for the Sportsmen's Association, which represents 40,000 shooting sports enthusiasts, said that "dark forces" were at play.
It also emerged that the Ministry of Defence has given VIP tours of RAF Leeming in North Yorkshire as prizes to raise funds for the countryside campaign. The MoD said it was designed to improve relations with the local community and had "no political overtones whatsoever".
The Sportsmen's Association is providing stewards for the weekend march which is expected to attract up to 250,000 to London in a protest against the threat to traditional country life.
But Mr Yardley said most would have "no idea" of the politics behind the scenes. He believes his organisation has been marginalised by those supporting the interests of fox-hunters and landowners. "I think there are some very powerful business and landowning interests who are taking over the political control of it," he said. "The Conservative Party is jumping on to this bandwagon."
The Tory party leader, William Hague, will attend Sunday's march in a personal capacity and the Tories recently launched a Countryside Campaign to protect the green belt. By contrast, the Government is only sending junior agriculture ministers.
Major landowners giving fund-raising support to the march include Minister Michael Heseltine, the former deputy prime minister, who offered a tour of the arboretum at his country home as a pounds 450 prize in a fundraiser organised by the local hunt. He also paid pounds 500 into the march fund for the prize of a gardening consultancy.
Mr Yardley claimed his association had established the popular movement for country rights when it held a succession of marches in London a year ago in protest at legislation to ban handguns.
Then in July, the newly formed Countryside Alliance organised the Countryside Rally, which was supported by the Sportsmen's Association and attracted 120,000 people. In September, the Sportsmen's Association staged another London march, which Mr Yardley claimed was undermined by powerful interests.
He received several telephone calls, including one from a "senior figure in the Conservative Party", warning him to cancel the march. The Conservative Party has denied hijacking the campaign and said the event was run by an "independent organisation and we don't give them any support".
Janet George, of the Countryside Alliance, which organised the march, said: "There are one or two organisations who should try to stick to the spirit of the march and not try to make political points."
In The News, page 3; David Aaronovitch, page 21Reuse content