I would probably renew my medical before I did anything else. If you didnt hold a class 1 before, then I would seriously consider doing that now before going any further, assuming of course your going down the CPL/ATPL route.
For starting ATPL theory, you need to hold an ICAO recognised PPL. But im sure you knew that already.
If you need to do an initial Class 1 Medical then its a trip to Gatwick and several hundreds of pounds to the Doc. It is however peace of mind if you get the all clear!