Hi all, I'm planning to book an open-jaw trip in economy for LHR --> SIN; BKK --> LGW with 2for1 voucher. No issues with the distance of the surface sector, and seats for both flights are still available since I want to fly in Q4, but wondering how will the taxes be priced when I call the BAEC (Gold line if that matters)? LHR-SIN is £250 in taxes, whereas BKK to LGW is £42 but not sure if that's only for one-way tickets pricing? I'm concerned that if I call BAEC they'd price taxes as £250 (SIN) + £200/250 (BKK) as for a return trip (am I right?).

I was considering booking two separate one way trips (with 2for1 applied to outbound) and then calling them to merge them and refund me Avios for inbound flight given the 2for1 voucher, but I read that only applies if inbound leg wasn't available at the time of booking due to T+355.

Any suggestions?