That's almost the polar opposite. Get up early, take exercise in LAX/YVR, eat a biggish meal 2 or so hours before departure. Get to sleep as soon as you can after take off, I drift off by reading Kindle books about Iranian social history, but anything mind numbingly dull will do. Sleep for as long as you can, at least 4 hours, but then mid Atlantic kick the brain into life with a film, exercise in London, more Iranian social history at midnight, job done. Again no alcohol, you can binge a bit on the pre flight meal, but make it digestible, pastas and other basic carbs, not an overload of protein. Then eat light on the flight and back in England for the first day.

I actually kick the CW footrest lever as soon as we are above 2,000 feet or so, and have everything in place to be vertical horizontal before 5,000 feet.