theres a few things to weigh up going into a first track day, your ability/experience,where do you rate yourself and how confident are you. What car will you be using, is it an every day car or simply a track car that you are going to chuck money at or just something cheap and cheerful that wouldnt be the end of the world, heaven forbid you crash it. As you're based in Sheffield have a search for a place called Elvington airfield not too far from you. They often have driver training/ track days. My old race driving coach Andrew McKenna once did race driving instructing there and taught me when I raced a peugeot 106 rallye in 750 motorclub stock hatch and a porsche 944 s2 in porsche club uk. Ive raced at oulton park, silverstone, snetterton, donington park, brands hatch, cadwell and mallory park. Cadwell, yes its a great track but probably a bit tight for your first one. I would describe it as a 'mini nurburgring' not a lot of run off area. Anyway, ask yourself those questions I listed and answer them. Hopefully you will make up your mind and best of luck to you, remember to have some fun and enjoy it, however I will warn you, once the bug has bitten I hope you have plenty of money as it is a very expensive and addictive hobby. Since losing my sponsorship I cant afford to race any more, but still love to attend track days and race meets.
Cheers, Mike