Why are you so keen to stay under the TMA instead of flying in it and getting a service?
For most of us, it isn't an option. London TMA is class A airspace which requires a valid instrument rating, but more importantly being in the vicinity of Gatwick, Heathrow, City, Southend, Luton and Stansted airports, in addition to smaller jet hubs such as Biggin, Oxford, Farnborough... There is considerable commercial traffic in the London TMA.