I think you'll find it's the present noise abatement procedure which causes this. If you want to complain to ATC Farnborough (not TAG) I can pm you a contact.
I'm not sure but I think the noise abatement procedure is notified in the AIP. When I was there, we usually cleared departures from 24 straight up to 3,400 with a 'best roc' through 3,000, but now I think the procedure involves an initial clearance to only 2,400 and many pilots might not check in with approach until they level off rather than call just after takeoff and get a continuous climb.