There are 20 wild animals currently performing at three circuses in the UK, a situation that Caroline Spelman, environment secretary, had sought to end.
The government fears it could face a legal challenge under the EU services directive if it goes ahead with a ban; others are sceptical.
Tory MP Mark Pritchard, who has won parliamentary time for a debate on circus animals on Thursday, believes his backbench motion already has strong crossbench support.
“There is overwhelming public and parliamentary support for a ban,” Mr Pritchard said.
“I hope the government will listen to the will of the country through elected representatives and bring forward legislation to end this outdated and cruel and barbaric practice,” says the animal-loving Tory.
Mr Pritchard is likely to be called to the whips today or tomorrow to see if a compromise will be struck as scores of MPs limber up to challenge the government.
The strength of political backing for a ban is reflected in an early day motion, signed by more than 200 MPs, calling for an end to what many see as a barbaric practice.
The debate will be one of the first uses of so-called “backbench debates”, which have recently been introduced to the Commons.
The last big backbench debate was in February on prisoner votes – proposed by Jack Straw and David Davis – saw a symbolic defeat for the government by a crushing 234 votes to 22.
“This is a bit like prisoner votes,” said one MP on Friday. “The government is going to face a defeat over this.”
This could create a headache for Ms Spelman, who has already endured one humiliating setback this year after abandoning plans to sell off the forests.
Defra said it intended to go ahead with plans to tighten the licensing regime governing circus animals. Mr Cameron is understood to support this approach, not least given the small number of animals kept by British circuses: “Tougher licensing should be enough to address the concerns that people understandably have,” said a Downing St aide.
Circus owners say their animals are well treated and the alternative – putting them in zoos – would be no more compassionate. But Defra’s own research has suggested that 95 per cent of the public would approve an outright ban.
Gordon Marsden, Labour MP for Blackpool, said that the government’s argument for not imposing a ban was “pretty thin”: “It’s a very unconvincing and bureaucratic defence of the position,” he said.
The campaign to change the law has been led by the Born Free Foundation, the RSPCA, the British Veterinary Association, the Captive Animals Protection Society and Animal Defenders International.
Will Travers, chief executive of the Born Free Foundation, accused the government of “mystifying intransigence”. “They claim that there could be a challenge to a ban in Europe but the EU Commission has clarified to us that wild animal welfare in circuses is a matter for member states, not the EU as a whole.”