As AA says....why not!?
The LCY zone and Thames is a good example.
If you ask for a radar service from this Non-LARS unit I will do so if not too busy with my primary task. If not, ident with a FIS can help you and me and others:
1. AS most people fly up the line now just East of LCY zone, we can warn the IFR inbounds about you (they start their descent just outside the zone at 3000 feet). If you are identified then your Mode C if on is also verified.
2. If you have asked for a RIS, but you are given a FIS, I will IF TIME PERMITS upgrade it temporarily to a RIS so that I can give accurate traffic info IF there is one BANG on your nose at the same level.
3. If after identification, you stray towards CAS, we will try and dig you out. Not too many people get prosecuted if we correct the navigation! Saves paperwork/avoiding action/legal costs!
As for flying up at 2400 (or the base of CAS) - well the base is in fact 2500 feet so you could be 2499! However, should you pop up to 2600 due to turbulence/thermal activity/too busy sightseeing and an aircraft gets avoiding action then you will probably be traced and asked for an explanation.
I prefer to be 21xx feet for that very reason....(as well as everyone else being at 2400..... You would be amazed at how many 7000 squawks I can see at weekends remaining at 2400 feet!!)