The chain, which offers pay-as-you-go membership and 24-hour gyms but cuts costs by only allowing members to sign up online, has grown from a single site in Hounslow, west London, to a 66-branch empire. Treharne plans to open between 15 and 20 new gyms a year working with Bridges — which has been with the company as a seed investor — and Phoenix, which invested in 2013.