Originally Posted by TyneTraveller

Unless I've misread the intentions here, I don't think it is advisable to attempt a back to back on the 21st. You will need to take the first flight of the day back to LHR from your chosen destination in order to obtain a sensible connection time for an 11am long haul departure. I certainly think the majority of the early domestic flights are night stops, so not suitable for the back to back option on the day. If you do the outward sector the night before, your options are far better in my opinion.