It could do, but I suspect not.
Looking at tracking sites, it appears that the return has been all flown at a lowish level.
In the event of an engine failure, normally one would expect the aircraft to descend to an optimum single engine level which may be at that level, but I would expect the speed to be higher than what you quote.
Furthermore, in a twin, an engine failure would se you landing at the nearest suitable airport, which from the turnback position would be somewhere like Bristol, and not London.
I tend to favour a pressurisation or window type of event, which could affect operating speed and level.
Time will tell!