Just so forum users have an idea of timescales for the interviews at the US Embassy in London.
I received my Global Entry CBP 'conditional approval' yesterday and immediately booked for my interview/enrollment at the US Embassy in London. The earliest date available for interview was Tuesday 13th of March 2018. However some dates after this date were already booked up. Overall though, there seemed plenty of availability upto the 3rd of May when the 'enrollment event' in London ends.
BM