Cheesychap,
As we have not met yet im unsure how much of this is serious, once you have met the guys you will realise that 99% of all conversations are tongue in cheek, personally you can tell when im lying cus my lips move, however as you cant see them........
I think Brian's list covered everything but on your specific points
Electric vest........ im assumimg thats a piss take as its 33 degrees 2mo and hot hot hot next week.
Layers under your J&T......... er nowt except your undies, my jacket has a waterproof and breatheable liner in, which i will leave in but the thermal layer wont be making the trip.
ambient temperature and wind chill..... you will be either sweating your cods off or dripping wet with the thunderstorms that are predicted ( but you wont be cold )
my only other weather proofing are a pair of rain over trousers, my Revit all seasons jacket im hoping will keep the rain out, did 6 weeks ago over there in the Thunderstorms.
This is meant to help believe or not, i promise not to start the piss taking until we have got worthing welsh drinking cocktails

that could be on the train over....
Lloyd