so you have to ask the question; in what capacity did the UK sign it - as a member of the EU, or as an independent member of the EEA in it's own right?

Yes, this another way of synthesising the issue. The UK is directly identified as a "Contracting Party" in the Agreement, independent of the EC (this is different from a ratification). My impression is therefore that indeed it is an independent member of EEA. But I agree this is likely to end up with the ECJ.

You might find me At The Edge Of Time.