Tom, a commercial licence requires a class 1 medical. A PPL needs class 2. Some folk are unlucky and cannot get a class 1 irrespective of their efforts. No need to do it right away, but think about getting a class 1 even for the PPL so that you know you don't have some impediment. Eyesight is an obvious one.
One other thought...when you do your PPL, you may find an instructor who flies commercially. Our club has several - they do flight training because they love it - and they fly airliners for a day job. It's nowhere near Cornwall but I'm guessing it's not unusual. I'm not saying the training is any different, but you will doubtless pick up tit bits about real life commercial flying.