Amendment to Hunting Act would allow up to 40 hounds to flush out a fox to face waiting guns

A growing number of Conservative MPs have warned David Cameron that he risks losing a vital Commons vote if he pushes ahead with what they believe is an attempt to weaken the ban on hunting to woo rural voters away from Ukip.

Environment officials are examining what they describe as a "viable amendment" to the Hunting Act, which would allow up to 40 hounds to flush out a fox to face waiting guns rather than two, a move that critics claim would effectively reintroduce hunting with hounds "through the back door".

The Blue Fox, a group of anti-hunt Conservatives, said that 27 Tory MPs had contacted them to declare their disquiet over the developments, with another significant cohort yet to decide whether they will vote against the plans because of sizeable pro-hunt support in their constituencies.

The proposed amendment would be likely to use a parliamentary device known as a statutory instrument to amend the contentious 2004 act. Opponents of foxhunting predict that the move will be unveiled next month and it is has been claimed that the environment secretary, Owen Paterson, has tried to canvass support among MPs of all parties.

However, the plans will face sizeable opposition from within Paterson's own party. Lorraine Platt of Blue Fox said more MPs were coming forward to voice their opposition, citing a statement forwarded to her by Mike Weatherley, MP for Hove and Portslade, which read: "My support for the Hunting Act remains completely unchanged and I will certainly vote against any attempts to weaken it."

Anti-hunting groups believe that any attempt to amend existing legislation would be whipped, meaning that Conservative and Liberal Democrat MPs would be told to vote with the government. Cameron promised last week that MPs will be handed a vote on whether to relax the hunting ban.

A letter from Glyn Davies, Tory MP for Montgomeryshire, to a fellow Conservative MP that has been seen by the Observer says that "all that has ever been discussed is a minor change which aligns the situation in England and Wales with that in Scotland".

The devolved Scottish parliament passed its own hunting legislation in February 2002, making it the first part of the UK to ban traditional foxhunting, while still permitting hunts to use packs of hounds to flush out foxes to face guns.

In a letter dated 17 March, Davies writes: "Suggestions by LACS [League Against Cruel Sports] and others of 'repeal by the back door' are bizarre, as what is being proposed is a measure that they themselves support in Scotland." The league, however, has accused the MP of "trying to mislead" and has released a statement denying that it supports hunting with a pack of hounds. It said: "We are strongly opposed to any amendment which would effectively allow traditional hunting with a full pack of hounds to openly take place in the countryside. The amendment being pushed would lead to this."

Platt said her group believed that the amendment idea, put forward by Welsh hill farmers to defend their flocks from foxes, was a "device to bring back hunting with dogs through the back door".

She added: "What it will do is allow a full pack of hounds to flush out a fox. It will almost be impossible to shoot that fox because you can't control a pack of hounds in the same way you can control two dogs; you wouldn't be able to hold off those packs of hounds. It's not an acceptable amendment and we urge all Conservative MPs not to back it."

Joe Duckworth, chief executive of the LACS, said: "We know that moves are afoot to weaken the Hunting Act through a back-door amendment. The government need to stop dancing the political 'hokey cokey' and come clean about their intentions on bringing this forward. If they have the courage of their convictions, they would fulfil their coalition agreement promise and hold a free vote on repealing the act and end this constant uncertainty about its future."

A spokesperson for the Department for Environment, Food and Rural Affairs said: "A number of Welsh farmers have brought this issue to our attention and we are looking at it."