Cash machine. Subscription model. Reinvesting into new sites. Only major competition is Puregym.
Interesting suggestion, a lot of people I know go to The Gym, although I personally go to Pure Gym.
If there was a recession, or Brexit caused adverse effects, my worry would be that consumers would cut back on spending and subscriptions, like a gym membership could be one of the first things to go.
But undoubtedly gyms are very popular, and in this day and age many people are in to fitness.
There are other commercial chains of gyms. What makes you think The Gym stands out