Isn't there a small barbers in T5 arrivals?

a gym would be lovely sometimes, although having wet / sweaty gym gear in my bag for a load of travel might not be a great thing.

I've used the hostel option a few times for clothes washing.
Handy on say a week long trip, hotels cost ££££, and you sweating in some tropical climate and going through t-shirts quickly. Don't think LHR is really somewhere I would do any washing.

Some hotels do have laundry rooms.
The HGI at OTP has one. Various Hamptons etc. in the US ss well.