If it's a busy Premier Inn, you can time it and go through at the same time as another guest. Otherwise, it's the WGs responsibility to figure out access.
The problem for them is staying off reception's radar if they're meeting a series of men for short times. One wg would wave discreetly from behind the partition and open it without being seen. Another had actually worked out a deal with reception and they just let me in.
Unpredictable, that's why wgs usually choose more discreet hotels.