Thanks Dave, that was very helpful.
None the less....I have reached a dead end and despite my initial plans I am not going to pursue this further.
Basically Fair Trading put me on to the fuel testing guys, but they do not beleive the sample will be accepted as valid because I have not stored it properly (water bottle, not cleaned out, stored in sunlight).
I would suggest anyone else who has a similar issue keep a good fuel sample in a proper fuel safe container, and have it tested ASAP after the issue. I left this too long, bad luck for me.