Can you explain what public body means and its relevance to the directive - you sound like you know far more about this and I'm curious.
There isn't a list of what is and isn't a public body, but generally if it is a public body then they'll be calling themselves such. This would include the NHS, central government, county councils, the tax man, schools (obviously excluding private schools) - as a basic rule organisations that get most of their funding from the government. The reason that public bodies are important is to do with how a Directive works.
Basically a Directive works as a set of minimum levels that the national law of member states must meet. Lets take, for example a Directive decided on 1st September 2009 saying everyone must give me £1 a post. Member states must then create a law that gives me at least £1. They could create a law giving me £2, but not one that only gave me 20p. Until there is a national law then the Directive is meaningless - think of it as an order to the member states to go and create a law.
The question then arises of what happens if a member state decides it's just not going to create that law (the UK has done it several times). Well I couldn't then sue you for not giving me £1 a post because it's not the law in the UK. If I could then that would mean that you'd have to go and read every single Directive, which is unreasonable. If three years had gone past since the Directive (so it's now 1st September 2012) I COULD, however, sue any public body when they fail to give me £1. That is because, due to the government's failure to do as the EU says, I'm being disadvantaged - and the government (and thus public bodies as they receive government funding) shouldn't be able to profit from it. The government would then also get in trouble with the EU and get fined. The three year figure is because in some countries it takes forever to get legislation through so they need time - countries are penalised when they just ignore Directives, rather than just being a bit slow.
To take it back to the facts at hand. Say the government decided to create the NCS (National Camera Service) - a series of shops throughout the country selling cheap cameras. If there was a Directive saying you must get a minimum of 20 years warranty and parliament decides
'sod that, what a stupid Directive' then that will help the NCS because they then don't have to take back my 15 year old camera. Meanwhile public bodies in other countries are having to give that 20 year warranty, which is unfair. The EU is all about creating a fair, open market. As such, you could sue the public body and get your warranty. Meanwhile if you bought the camera from OcUK, well it's unreasonable of them to have to keep up to date with everything the EU does. It's not unreasonable to expect them to understand UK law though. As they're not in breach of UK law you couldn't sue them. Whilst they would be in breach of the EU Directive, for the reason we just stated, you can't sue them.
Hope that makes sense!