Check out the rules from the ANO.
You must have permission to enter an ATZ from whoever is responsible for it. That may be the airport owner who delegates it to an air traffic function or whoever. Think also about non-radio entry to an ATZ. Some of them require you to ring up beforehand: that is obtaining permission of the responsible person..
A MATZ does not require permission to enter it. Common courtesy/sense might suggest you should at least say where you're going to prevent surprises from noisy pointy jets.
In the case of Farnborough/Odiham: crossing the MATZ does not include permission to enter either the Farnborough/Odiham (or even Blackbushe as it is very close) ATZs unless specifically stated. It seems simple enough: two different types of airspace.