Originally Posted by
GUWonder
Due to boarding pass conformance checks at T5 even when doing terminal transfers from another terminal via tarmac shuttle buses, it's not possible for incoming passengers at LHR to get to the T5 train to get to immigration that way unless already airside in the departures area at T5 or unless having just arrived by plane into a section of T5. I only bring this up in case some think about doing terminal shuffles to try to get a faster passport control line.
That's not correct. If you are arriving at another LHR terminal (T2/3/4), you can if you wish follow signs for Flight Connections and take the airside transfer bus to T5, which drops you at the Arrivals/Flight Connections area in T5A. From there, instead of going with other passengers through connections security to connect to another flight (where your BP would be scanned for conformance), you can simply go to passport control and cross the UK border there. There is no train involved in this.
More detail available in the guide here:
A Guide to Connecting at LHR T5