Chris Mason: Row over Reform's mega donations has mileage in it yet

The £72m heading towards Reform UK's coffers from two British billionaires is transforming the debate at Westminster about politics and money.

In short, how should political parties be paid for, and by who?

It is worth setting out the law, in broad terms, now and how the government hopes to change it.

Right now, there is no limit on how much anyone, living in the UK or abroad, can give to a British political party as long as the individual is registered to vote in the UK.

But the government has been planning a change in the law for months, which would limit donations from Brits abroad to £100,000 each per year, backdated to 25 March this year.

But, crucially, the law hasn't changed yet and some of the key details in that proposed new law - such as what residency requirements would need to be passed to be classified as no longer being abroad - haven't been decided yet.

The reason for that date, 25 March, ministers argue, is that is the day a review by the retired civil servant Philip Rycroft was published, , external the first recommendation of which was that there should be "an annual cap on political donations from British voters living abroad".

On that same day, the then-cabinet minister Steve Reed told the Commons , external that cap would be £100,000 per year. He also added that it would "apply retrospectively" from that date onwards, even though the law at the time, and indeed now, has not yet changed.