Arrive in HongKong, Stay for 2 days; depart via Beijing (2 hours layover) to London - Visa reqd.?

No, you do not need any kind of visa because your transit in Beijing will be covered by 24 hour visa free transit. All you have to do is to be very, very fast at Beijing airport in order to catch your flight to London. I hope you are traveling on a single ticket and that your baggage will be tagged all the way to London because you would not have enough time to perform all the formalities if this is not the case.