It is a tricky one, because for smaller parties, if they can attract one or two larger donations - of the 100K level - it can make a huge difference.
I do think they should only be allowed to take donations from UK residents. And that means where the money originates in the UK - so a donation form a UK company that happens to be the same as a donation made to that company form abroad not allowed.
I totally agree that they should be very strongly policed.
But there is a bigger question of the whole role that money is playing in our politics. We need to get it out, but that is not going to happen.