Hi Rob
You could try hooking up with BrightonMTB. I sometimes ride with them on a Thursday evening, although the ride doesn't end at the pub. If you can travel a little further afield then SussexMTB do a Tuesday night ride and it nearly always ends up at the pub but its over Worthing way.
The Brighton MTB Thursday rides tend to be a bit more chilled and with more singletrack than the Sussex MTB Tuesday night rides but both are good fun with a great bunch of peeps. Both groups also have weekend stuff going on as well.
Check em both out and see how you get on.
Look forward to bumping in to you with one of the groups sometime 😛