Originally Posted by emcampbe

just have a copy of your SQ PNR and ticket. That’s all the agent should need.

note that whether your connection is 12 hours or less or slightly over 12 hours could be a differentiating factor. My understanding is by default, UA won’t check bags for over 12 hours between flights, with some stations being exempted from this - SIN is one, and I just had, with some difficulty, this done on a 14 hour connection (somehow, the computer was telling the agents that my SQ [regular economy] fare was ‘not a valid class’, but eventually, it got done, with persistence from the amazing agent and supervisor at SFO helping me. If your connection, is say, 12:05, they may not try or even be able to it if they do. So if that’s the case, I’d plan to have to go through customs at LHR to get the bag and re-check, but hope that you don’t have to.

on that note, note that even if SQ desk is open at LHR to check the bag with, they may or may not actually check it if your flight is not theoretically open for check in. SQ at SIN will accept bags within 24 hours of flight, IIRC, but not sure if that works at their other stations as well. May want to find out from SQ.