I'm thinking of investing in a motorbike (petrol not electric) but not sure what the deal is, so a few questions hopefully someone can help answer

a/ is it legal for a foreigner to buy/own/register one?

Yes it is, I own one.

b/ what sort of license is needed (i only have UK car license at the moment)?

you need Chinese drive license "C1E" it's very important the last "E" that means you can as well drive motorcycle.

c/ are there restrictions on where/when you can ride in beijing?

there are 2 kind of plates you can have in beijing, A and B, with the B plate you can only ride outside 5th ring road, A plate you can ride everywhere, but never inside the ringroad, still ok to ride on the highways such as the one that go to the airport.

d/ i've been told if the motorbike is under 50cc (which apparently you can now get 48cc models) no license is needed, fact or fiction?

In this case the law turn out to be very strange, some models are ok like the dragonfly, but this model it's not allowed in beijing, anyways police can do anything about those things they're legal, other models like honda dio or yamaha jog are ilegal.

thanks for the help guys!!