Start with a trial lesson. Contact a flying club (I'm sure there must be one at Cardiff airport) and book for an hour. Let them know you want to fly more, and make sure you fly most of the flight. I always encourage trial lesson students to do the take off, but many instructors don't like to do this.
The next course depends on what you want from flying. If you only want to spend money towards a commercial licence then go to Gatwick for a class one medical. If you would want to fly as a hobby anyway, then don't worry about a medical yet.
Next book yourself onto a PPL course. If there is more than one flying school nearby then visit all and find which you prefer. Spend as much time as possible with pilots or at the flying club. You pick up a lot by being in the environment.
The next things you need will be to build your hours up to 150 and complete the ATPL groundschool, but that is something you will get to know more about as you learnt he PPL and talk to other pilots.