- If you are on the same plane (BA15/BA15) the short break in SIN is no issue as you get on exactly the same plane and gate you were off from. If you are quick you could go to a lounge (QF J, QR or BA J) but do not dally around as security is at the gate. Safest lounge will be the BA lounge as they will call the flight. They will make some announcement to be back at the gate in 30-45 mins but you can most of the time ignore that, and just look at the gate close time.
- You will need to do security in LHR connecting anyway, that said I would not bother with the arrivals lounge, just yourself through and then to the showers in Galleries South.
- As above you will have access to the Galleries airside lounge in LHR - just show your BP. Odd that it was in Y - is it an award ticket?

- If the flights are not on one ticket then let us know, as that changes a lot of the advice.

There are lots of threads on how to cope with the short SIN sector and the god awful BA arrival time into SYD. I would be focusing on that more than transit times.