Ok. I think I have a better understanding now than I did. Correct me if I am wrong...
The more active I am before sleep, the hotter I will be. To counter act this, cut down on activity before sleep. Seems obvious now I have thought about it.
Going to sleep wet will cool my body down. My GF isn't happy with this but now I can say its "Medicinal"
Having cold showers, or keeping myself cool, has the reverse effect. My body will need to work harder to heat up my body up back to normal hence generating more heat. So I can assume that if I keep my body 'hot' before sleep, my bodies cooling mechanism will kick in and therefore make me feel cooler.
Long term, if I want to condition my body to get used to the heat then in theory it is possible for the body to adapt to the higher temperature but as United Kingdom does not have extreme weather and is inconsistent as best, plus any adverse medical effects that may occur, this isn't really a solution to my problem.