Thank you for the quick feedback!
Yes, I have a hotel for the night, so when I check in for DUS the next morning I was wondering which lounge(s) I could use.
I definitely don't have a lot of LHR experience. Just a few visits a long time ago... I'm a FRA kind of guy....
I know I arrive (EY) at T4, and the next morning I go back to T5 for the BA flight to DUS.
Thanks again! Any particular "better" lounge to visit in T5?