It's one of the classic grey areas. The offence would be careless or dangerous, the rider will often try to fight the suggestion that they weren't in control of the vehicle by the fact that doing what they were doing wouldn't have worked without them being in control. Doesn't make them any less of a nobber (although my inner 12 year old does a little dance of joy most times I see it happen, cycles too.) but it may tempt the copper to go for a warning rather than a lot of paperwork... Also, the last comment, 'get out of the square mile & don't come back' he's just hoping the Met will nick the guy later, not that I'm saying City are lazy or anything!
The cop was doing fine until he said "get out of the square mile & don't come back" What is this a new sheriff in town. If the Police officer is ordering him to Leave the area then issue a section 27 notice if driving like that meets the criteria. I can't tolerate people in authority working outside their authority.