Thousands of innocent adults are being punished by constant ID checks that fail to tackle the problems of under-age drinking, a civil liberties group has said.

Adults should be "free to stock up on drink without being treated like criminals" and should be able to go shopping without having to take their passport for fear of being challenged, the Manifesto Club said.

Retailers should scrap "absurd" policies such as "Challenge 25" or "Think 25" in favour of a more courteous and common sense approach to enforcing the legal age limit, it said.

The situation is likely to get worse next month as changes to the law mean retailers will have to ask any customer who appears to be under the age specified in their own policy for photographic ID, rather than just anyone under the legal age of 18.

The new mandatory licensing condition "effectively turns supermarkets' already cautious policies into law", according to the group, which campaigns against the over-regulation of everyday life. It added that plans to double the fine for retailers who persistently sell alcohol to children to £20,000 are "disproportionately harsh".

The "unnecessary and patronising" blanket age-check policies reflect "a serious loss of perspective" as thousands of over-18s are being caught up in over-zealous policies that create the idea of alcohol as an illicit substance.

Dolan Cummings, author of the Manifesto Club report, said: "These adults are no longer young and feel that they have earned the right to be treated with some respect.

"It's not flattering, so supermarkets should stop telling us that it is. Constant ID checks create the idea of alcohol as an illicit substance, rather than as a normal part of adult life to be enjoyed in an adult manner."

A Home Office spokeswoman said: "The Government believes that regulation should only be used as a last resort, and that alternatives to regulation should be used wherever possible. We want to give people the chance to comment on the necessity, cost and impact of the provisions outlined in the Mandatory Code on Alcohol Sales.

"The Government is currently consulting on a range of proposals to tackle alcohol-related crime and is seeking views on the mandatory code. We welcome all contributions to the consultation, which will close on September 8."