As Nuts magazine hits back at the Co-operative's "ultimatum" to give lads' magazines six weeks to cover up or else be taken off the shelves, Channel 4 News asks if other supermarkets will follow suit.
The publishers of Loaded, Front, Nuts and Zoo, have been given until 9 September to deliver their magazines in pre-sealed "modesty bags" designed to obscure the front covers.
The Co-op said that in the last year it has sold around 500,000 copies of the magazines – roughly a fifth of the combined sales of the four magazines, according to Channel 4 News estimates.
The Co-op, which has 4,000 stores across the country, said it had received complaints after its previous policy of using opaque screens was found to be "not foolproof".
It said many of its stores are smaller convenience shops, with low-level shelving units which can be easily viewed by children.
The display of magazines is a matter for each individual retailer, according to the National Federation of Retail Newsagents.
There is a voluntary code of practice advising that adult material should be placed on the top shelf – and it recommends that "men’s lifestyle" magazines should not be put next to children's titles or at eye-level or below.
The Co-op told Channel 4 News that the publishers of the four lads' mags have not yet agreed to the measure, but it was "in a dialogue with them".
But a spokesman for Nuts magazine, which is published by IPC Media, said: "It is astonishing that the Co-op has issued this ultimatum through the media without consulting the publishers - their key business partners - this is not how we prefer to do business."
The sale of lads' mags has been in huge decline since the widespread use of the internet.
At its peak in 1998, the original lads' mag, Loaded, drew more than 450,000 readers a month. Its readership had dropped by almost 90 per cent when it was sold by IPC Media in 2010.
The latest available figures show it had an average monthly readership of 34,505 in the second half of 2011. It is thought that reader numbers may have plunged to less than 20,000 since then.
The figures for Front, Nuts and Zoo also make for grim reading. According to latest ABC circulation figures, Nuts' circulation has fallen by 30 per cent in the last year alone – to 80,186 per month.
Zoo's monthly circulation has dropped by 20 per cent over the same period, to 44,068 a month, and Front has seen its circulation fall by 12 per cent to 30,061 readers a month.
Last year, Loaded's former editor Martin Daubney said the massive sales once enjoyed by the magazine were "always down to pictures of scantily-clad women".
He wrote in The Daily Mail: "If we were classified as 'top shelf', we'd have been put in opaque plastic gas like the pornographic magazines, which would have been commercial suicide".
Legally, it is an offence to display indecent matter in a public place, so it is a magazine's cover – rather than its contents – that matters.
“Indecency" is not defined by law, but publishers have to cover up anything that might be deemed obscene – "having a tendency to deprave and corrupt" – in order to avoid prosecution.
Though not traditionally "top shelf" material, men's lifestyle magazines - or "lads' mags" – have long been criticised for being displayed in places where they can be seen by children.
The Co-op's move to cover up lads' mag covers is in line with an independent review commissioned by the government.
In 2011, the Bailey Review by Reg Bailey, chief executive of the Mothers' Union, on the commercial pressure on the sexualisation of children, recommended modesty bags or boards, concluding that "retail associations in the news industry to do more to encourage observance of the voluntary code of practice".
Jo Swinson, minister for women and equalities, said: "Many parents aren't comfortable with the way that sexualised imagery has become like wallpaper - everywhere from the bus stop to the corner shop.
"Exposing children to lewd pictures that portray women as sex objects is not appropriate. That's why the Co-operative's decision to implement the Bailey review recommendation for publications with overtly sexual images on the cover to be displayed and sold in modesty bags is very welcome.
"Adults should be left to make their own decisions about what legal sexual images they look at, but the place for these is not next to the sweets at children's eye-level. I hope other retailers will follow the Co-operative's lead."
However, the Nuts spokesperson said: "The solution the Co-op has created doesn't deliver for anyone; it doesn't work for consumers of men's magazines, it doesn't work for publishers and it has not been welcomed by the feminist groups they were so keen to appease".
They added: "The content and covers of Nuts are perfectly legal...Nuts' content is broad and covers sport, gadgets, amazing photographs, games, trivia, humour and women. Responsible men's magazines - like Nuts - celebrate women - and to suggest otherwise insults the adult men (and women) who buy, read and enjoy these products".
Supermarkets account for just under half of all magazine sales, according to the Professional Publishers' Association.
Of the big four supermarkets – Tesco, Sainsbury's, Asda and Morrisons – Sainsbury's is the only one to enforce the use of modesty covers.
Asda and Morrisons told Channel 4 News that they had no plans to introduce the measure, with lads' mags currently displayed behind cardboard and opaque Perspex screens respectively.
Tesco meanwhile told Channel 4 News it was "looking into" the issue. "We are also talking to our customers, to find out what they think, before we make any decision about next step," a Tesco's spokesman added.
Sophie Bennett, from Lose the Lads' Mags campaign group, said the Co-op could still do more. She said: "Thousands of people have called on retailers to stop selling lads' mags like Nuts and Zoo.
"The Co-operative's actions show our voices are being heard. Yet the Co-operative are attempting to sell their customers short.
"The so-called 'modesty bags' they are demanding from publishers are designed to allow the Co-operative to continue profiting from sexist, harmful lads' mags - but just a bit more discreetly.
"That's not what corporate social responsibility looks like."