I will have a few hours to kill between flights at T5, and was wondering if it was at all possible to clear security, settle down in the lounge, and then exit for a bit and clear security again?

I know it's not been possible at the other LHR terminals, but I wasn't sure of the arrangement they had at T5, it having both domestic and international flights under one massive roof.

Is it a typical American-style setup (where you can exit and re-enter) or once I'm in, I'm in?

Thanks all!