I'm planning on flying IAD-LHR-BOM, UA to LHR, then onwards to BOM on BD.

I'm considering taking the daytime flight across the Atlantic, arriving around 2200 into LHR, giving me about 11 hours till the 0920 BD departure the next morning.

Since I'm *G (United Prem Ex) I will have access to BD's diamond club lounge at LHR. Is it open overnight? Since I don't sleep too well on airplanes, I thought if the lounge is open, I could actually get some decent sleep time at LHR between flights.

If it's closed, any other lounge options available in T1 for the overnight hours?

Failing that, is T1 alive enough overnight that I could keep myself occupied (shops, etc.)? Any comfy places to sleep? Or would grabbing a hotel room near the airport or heading into London be my only other options?