Originally Posted by
BA6501
The bus should well be faster than the train combo. If you are HBO or your bag is checked through then you can arrive in T5, go to Flight Connections and take the bus to T4 and clear immigration there.
Correct. If bags are checked through - which will only happen if on a single PNR - then the airside connections bus and then going landside at T4 should be easier, although I don't know how the immigration queues will compare at T4.
Otherwise the landside 490 (or 482) bus is simple enough albeit not fast. No oyster/contactless required.