Thanks for the reply stacey_s.
Further interrogation of my father has uncovered the possibility of it being either a stolen helicopter or a jailbreak ???? He looked at the photos of the Hughes 300 and Bell JetRanger and said that the aircraft that he saw were all more like the Bell and not with a bubble canopy....
Apparently the helicopters seemed to come from Battersea Heliport direction (my guess) and heading south (of London) at much greater speed than normal, much lower than normal, perhaps up to 5 in number....
Any help to alleviate a father/son argument appreciated.
Regards
SHJ