Originally Posted by DeathSlam

The confusion may be that your car\hotel needs to be within the trip duration.
Previously some people were staying at an airport hotel the night before\after their flights (i.e. in the UK prior\post an international flight) and counting that as part of the 5 nights. That changed maybe 18 months ago.
However you can still fly a domestic to Heathrow and stay in a hotel or arrive in Heathrow stay in a hotel and then do a domestic. The domestic flights count as part of your trip so the hotel nights *do* count then.