A council has been accused of overstepping the mark by urging licensees to sign a contract forcing them to run a Challenge 21 scheme.
Bexley Council has written to every licensed premise asking them to sign an Acceptable Behaviour Contract covering the "responsible retailing of alcohol".
It means pubs would be legally tied to run the Challenge 21 initiative, which encourages staff to ask for ID from anyone who appears under 21.
The contract also covers training on refusing to serve somebody who is already drunk.
But the British Beer & Pub Association (BBPA) has urged its members to ignore the letter.
Martin Rawlings, the BBPA's director of pub & leisure, has written to the council's licensing department, claiming the contract is "in direct contradiction with both the letter and the spirit" of the Licensing Act.
By forcing pubs to adopt Challenge 21, the London council is "going beyond what the law requires", Rawlings states.
"It is a voluntary measure and should not itself become on obligation on a business," the letter says.
It also criticises the council for not encouraging licensees to seek legal advice before signing the contract.
However a spokeswoman for Bexley Council said it had received an "encouraging response", with around 20 per cent of the contracts signed. "There have been no direct refusals," she added.
"The decision to sign or not to sign may be taken into account if there are any future problems associated with the business and considering whether or not the business is 'promoting the licensing objectives'."