Really sorry to hear your woes. It is such a pain in the neck when the warranty which is there to help you ends up causing loads of hassle.
I agree with Graham, get it all written down in a succinct letter stating all the facts with ref to trading standards and this should make them do something.
Makes me realise how lucky i was with my nissan garage. Although i see alot of hate for the nissan dealers here i would have to stand up for the Tunbridge wells branch as they were absolute stars. viewtopic.php?f=9&t=40880&start=15
I know my experience won't help in your situation but if anyone else is looking at getting any work done or buying a car and want a Nissan dealer that actually knows what they are doing go here.
Hope you get your problems sorted soon mate, theres nothing worse than having something that could be resolved so simply really sour your 350 experience.
good luck