It depends which type and level of motor sport you want to compete in. For a lot of grass roots motor sport all you need is to be a member of a local motor club, which you can join on the day. However for Racing, Rallying, some Karting and a few other disciplines you need an MSA Competition Licence. You also need a licence for any national level events or championships. To find out more, take a look at the Get a Competition Licence page.