Seen over East London

I have only just got home after seeing what I can only describe as the most Reckless/ Skillful flying I have ever seen but as it was over a built up area I think I will go with the former What appeared to be a Augusta 109 flying behind a twin engined aircraft with the blades of the 109 as close as 10ft from the tail of the twin which was being thrown into tight left and right banks at low level. What was going on I have no idea, My son who also saw this phoned me he said he thought the 109 was in police markings but the Met police do not use 109 the only thing I can think of is the RAF 32Sqn who’s markings do look like the old Met colours and fly the Augusta 109. Anyone have any idea what was happening?