The pair of passers-by are believed to have leaned on the site hoarding in the early hours of Saturday before falling through and into the basement near Euston Station.
The couple were British Transport Police officer Gavin Brewer, 32, and his TV engineer boyfriend Stuart Meads, 34.
The residential site was run by a small local contractor.
The hole the pair fell through is believed to be an uncovered roof light for a basement flat.
A Met police spokesman told the London Evening Standard: “Enquiries continue to establish how both men came to fall. At this stage it is not believed anyone else was involved in the incident.”