The Co-operative will no longer sell Nuts magazine after the title rejected an ultimatum to use "modesty bags".

The retailer, which describes itself as one of the UK's largest magazine sellers, introduced opaque screens on shelves last month to shield children from "lewd pictures" on front covers.

It comes amid increasing debate about the effects of sexual images on children, with David Cameron recently setting out a raft of reforms which will introduce family-friendly filters that automatically block internet porn unless customers choose to opt out.

A spokeswoman for the Co-operative said: "Our position has not changed. If Nuts and Zoo, or any of the other publications, Loaded and Front, do not put their titles into modesty bags by the date we've given of September 9, we will no longer sell the magazines."

However, Nuts publisher IPC Inspire described the ultimatum as "an unreasonable attempt to prevent shoppers from freely browsing a legal magazine that is already displayed according to Home Office guidelines".

IPC Inspire managing director Paul Williams said: "The Co-operative's knee-jerk attempt to restrict access to a product that consumers have enjoyed for nearly a decade is wrong.

"Nuts takes its obligation to craft products that are right for consumers and retailers alike and for a number of weeks now we have had new covers in place, which have a more conservative tone. We are delighted with our readers' response to the new covers and last week's issue was our biggest-selling since February.

"The objection that niche lobby groups have against certain sectors of the media should not mean that the right to purchase a perfectly legal product is restricted for the over half a million Nuts readers.

"As has been widely reported in the media in recent weeks, this is no longer a question of whether or not you like men's magazines, it is a question of how far you can restrict the public's ability to consume free and legal media before it becomes censorship."

Following the Co-operative's announcement, Tesco said it would sell lads' magazines only to over-18s.