Here's my tips:
First on long flights reset your body clock before you leave - when I fly to the UK from the US I always take the late afternoond (5PM or later) flights and wake up at 4AM so I can sleep and be adjusted upon landing

Then on the trip I use EmergenC (or other hi vitamin powders/pills) I do 2 a day on work trips where I know I'm going to be out late drinking/eating and needing to get up early for work.

I know this might be hard to source in the UK (I've brought many a bottle to my UK co-workers since amazon.co.uk doesnt seem to carry it) but LyteShow is a god send (https://www.amazon.com/LyteShow-Elec...dp/B00EISFBYA/) and the travel flask makes it easy to transport; do one cap full with a bottle of water before bed and one in the AM - its like a magic eraser for 10 G&Ts.

Then Water, water and water drink lots before bed, on the plane and in the morning.

Lastly, it takes a bit but you kinda just get used to it - the human body is a nifty organism that adapts so initially it will suck but eventually you adapt (hopefully)