I’ll be honest, I don’t know the area well. Anywhere between southborough library and city centre I think. Do Puregym do day pass stuff? Can’t see anything on their website.
Looks like the Pavilion which is by the shopping centre does pay as you go. It's pretty pricey at £10.50 though. I've never been, I take my son swimming in the pool at weekends so can't say what the gym is like.
Depends on where in Bromley. It's a big place. Borough or Town of Bromley or City centre? If you're in city centre , there's a Pure gym.