The men have been charged with an offence under Vagrancy Act 1824 s 4, namely that they were found in an area, Iceland, for an unlawful purpose, stealing food. In fact, it is said that they were taking food items out of a skip, prior to them presumably being thrown away.
The Guardian has a report of the story here, which is worth a read.
UPDATE: There is a press release from Iceland which makes clear they did not call the police and are seeking clarification as to why the CPS believe it to be in the public interest to prosecute.
UPDATE 2: The CPS have confirmed they have dropped the prosecution. See the press statement for details.
There are a number of issues here, which have been discussed in case law, some of it, recent. These include what does ‘found’ mean, what does ‘unlawful purpose’ mean and when does the unlawful purpose need to exist.
Those wishing to do some further reading may want to look at the following cases:
L v DPP 2007 EWHC 1843 (Admin)
Smith v Chief Superintendent of Woking Police Station (1983) 76 Cr. App. R. 234
Talbot v DPP  1 W.L.R. 1102
One interesting point that appears to arise from the Smith case is that the unlawful purpose must be criminal, and not merely a wrongful act such as a tort (e.g. trespass). So consider the situation where the unlawful (criminal) purpose is said to be theft.
Does that then require an evaluation of the offence of theft?
The unlawful purpose of committing theft
Theft Act 1968 s 1 defines theft as ‘dishonestly appropriating property belonging to another with the intention of permanently depriving the other of it’. Section 7 sets out the maximum sentence of 7 years for a person convicted of theft.
Sections 2 to 6 define the elements of the offence. All five elements must be proven in order for the offence to be ‘made out’. The only one we are really concerned with is the first.
A person is not dishonest (for the purposes of theft) if he appropriates the property:
(a) in the belief that he has in law the right to deprive the other of it, on behalf of himself or of a third person; or
(b) in the belief that he would have the other’s consent if the other knew of the appropriation and the circumstances of it; or
(c) in the belief that the person to whom the property belongs cannot be discovered by taking reasonable steps.
So there would be problems showing that the ‘thief’ did not believe that they had the consent of either the council responsible for emptying the bin or the supermarket who placed the property into the bin.
So if it cannot be shown that the individuals were in the area specified with the intention of committing a theft (because they believed they had the consent of the owner) then it would appear that they are not guilty of an offence at all.
A final thought.
The Full Code Test, emlployed by the CPS when deciding whether to charge someone is as follows.
The evidential stage: Prosecutors must be satisfied that there is sufficient evidence to provide a realistic prospect of conviction against each suspect on each charge.
The public interest stage: In every case where there is sufficient evidence to justify a prosecution, prosecutors must go on to consider whether a prosecution is required in the public interest.
Perhaps it is necessary to add a third limb to this test – the idiot test: ‘could someone legitimately call me an idiot for pursuing this prosecution?’ It might save a few quid (and keep the naked rambler out of jail too).