To the person who says "if they were well paid before what happened to all their money" (sorry can't remember who) the answer is simple:
When candidates are running for parliament, before they are elected they are paid nothing.
They cannot claim any expenses.
Becoming an MP is expensive.
They give up work, and work entirely for free on the campaign. They pay to go to endless events & fund raisers.
That IMO is the main reason why there are few MPs who were eg teachers, nurses etc. because how many employers let you have weeks & months off to campaign? How many people can afford to take several months off work totally unpaid with no definite job at the end?
My DH is standing for parliament in May. If he wins, it will be a pay cut from what he used to earn. But at the moment, he earns nothing at all, and hadn't done for several months.