Are we supposed or expected to deduce from this that the Co-Op failed to "sign up"?

Local businesses have also reported positive effects, with surveys revealing a 20 per cent fall in the number of people stating they witnessed “a high level of street drinking around their premises.” But there was no change in the number of reported crime and anti-social behaviour outside stores owned by the Co-op. Police said that was against a background of falling incidents of crime and anti-social behaviour across the town.

Well if we did, we would be wrong !  Because ...

The experiment was launched by police and the Co-op in September amid concern at the behaviour of itinerant drinkers intoxicated by the likes of Tennent’s Super and Carlsberg Special Brew.

And it has been a roaring success (except, as previously noted, outside Co-Op premises, sadly) :-

At its outset, 53 stores halted the sale of cheap beers, lagers and ciders with an alcohol volume of at least 6.5 per cent. Now, 80 shops are taking part including Tesco, Debenhams, M&S, BHS, Waitrose, Sainsbury’s and Aldi, equating to two-thirds of the town’s 122 stores.

Updating the public on progress, Suffolk police said that between last September and this March the public had reported 94 “street drinker events” to police, compared with 191 events during the same period in the previous year, a drop of 49.2 per cent.

and what does this tell us ...

“Our results directly related to this campaign in relation to crime and ASB [anti-social behaviour] are limited at this point, but are set against the backdrop of fantastic work carried out by police and partners to tackle issues connected with street drinking in Ipswich. Reducing the Strength will add to these results and will help in providing these vulnerable people with routes out of their chaotic lifestyles.”

Er, pass, at this stage but much more importantly

Assistant Chief Constable Newcomb added: “There are still a third of these stores in Ipswich that are continuing to sell these items however, and we will now work with these businesses, along with our partners, to further discuss the benefits of the campaign.”

"further discuss" eh ?
  
"Would Sir/Madam care to try and put up a plausible reason why he/she is quite clearly continuing to sell these perfectly legal items in their store? "

"What do you mean 'we didn't actually stock them until all the other stores decided to stop selling them, and we sell quite a lot, actually’?  What kind of attitude is that?  Commonsense?  Now, don't try and get clever with me sunshine, else I might be minded to have a word with the licensing committee!  Oooops, now mind those stairs..”        

Street disorder drops after super-strength alcohol ban