This question already has an answer here:
I am flying Delhi-Lisbon and have a transit in Heathrow. My jet flight from Delhi arrives at terminal 4 at 5:40 PM and I have a TAP Portugal flight from Terminal 2 at 7:55 PM. This is single e ticket with both flight segments listed on the same ticket, so I am assuming my baggage will be checked through to Lisbon.
Do I need a Visa transiting at Heathrow and also is this enough time to make the connection? I am an Indian citizen with a valid US visa, so technically I am expecting as per UK website. But I am not sure given the fact that I need to take a train/bus to change terminals.