I have a round trip flight from the US to London. My plans changed and now I'll be flying out from London to the Schengen Area (Barcelona). My flight from US arrives at LHR (terminal 3). I have a separate booking of a flight from LHR to Barcelona ( departing from either terminal 3 or 5). My flight to Barcelona departs on the same day as I arrive. Similarly, on the way back from Barcelona, I fly in to LHR and same day depart out to the US from LHR.
My worry is my flight to/from Barcelona fro/tom LHR is not on the same ticket as my round trip flight from the US to LHR. I have a valid schengen visa and a US visa, and I'm an Indian citizen.
Do I need a UK transit visa? Will I have to cross the immigration border in this case? Say if I have to change terminals to get to my other flight? I do not plan to check in bags.
