seeing and hearing the new aircraft operating above London and the southeast
Well, if the Exeter BK117 is anything to go by, you'll certainly be hearing them. By far the noisiest emergency services heli I've heard in UK service. Was walking the dog on Dartmoor t'other day when I first picked up the sound of that tail-rotor. Four minutes later the aircraft flew past (half a mile south) at max chat. Not sure what speed they cruise, but something that can be heard 7+ miles away ain't going to be music to Red Ken's sensitive lugholes.
Enjoy the new kit, hope the performance is up to the jobs you have in mind.