I looked up Micheal Ellis, whom Chestnut mentioned as exemplary.
He no longer works as a barrister. However, he does hold shares in two companies. The register doesn't say how much he earns from the shares.
I'm not disputing that Mr Ellis is a good MP and not suggesting he's doing anything wrong, but the point is that he could be drawing a significant income from those shares, without actually working. Any MP with a small business could do the same.
I think any legislation would need to be more complex than just banning paid work. I don't think it's as easy as people think. A number of MPs own property, which presumably wouldn't count as "work". Boris Johnson gets paid royalties for work already written before he became an MP, which couldn't be stopped either. That would work well for any pop star or writer who wants to be an MP.
Something does need doing, but I'm not an accountancy/finance expert, so I'm not quite sure what. Like some others, I think the salary should increase (the metro mayors get paid more), but there need to be some restrictions on outside income. Maybe there should also be league tables of performance, based on number of votes cast, constituency surgeries, etc., as there are for schools and hospital trusts.