All you need to become a councillor is free time and a bit of ass kissing in the local party.
There's a fair few that are plain crooks in it to make money, supported by those that love the sound of their own voice, are easily flattered, totally immune to boredom and too dim to realise who the crooks are or what they're up to. And from personal experience there are as many Labour crooks as Tory, although not Liberal, I suppose they don't provide an obvious route to opportunity.