The British tendency now is for nobody to be allowed in as a candidate unless they have been following a career dedicated to politics. They may be allowed to have a notional career at the Bar, for example, but even being a trade unionist does not seem to get you preference in the Labour Party, as it once did. Jack Dromey is the last in that category that I can think of.
There is a depressing fashion for choosing candidates who have been in the party machine straight from university, as researchers and assistants, before being given a losing seat, to blood them, and then a winnable one.