In 2013, Gillies relocated to Singapore where he is now a “private wealth manager”.
Although he lives overseas, he is still able to donate via his companies, as they are registered and do business in the UK.The problem is that he isn't able to "donate via his companies" at all. A quick look at section 54 of the Political Parties, Elections and Referendums Act 2000 shows that individuals who are on the electoral roll can donate, as can companies carrying on business in the UK (and a few other entities). What you can't do is use a company carrying on business in the UK as an illicit channel for a donation from an individual who isn't allowed to donate in their own name. That's covered in section 61 which basically says that if you try to find a way round the rules you're committing an offence.
So, you can believe that a company where the turnover is only £6k a year happened to have £20k hanging around for political donations this year (that'll be three years and four months worth of income just sitting waiting - you can see why a company would just have that sitting about) or possibly, just possibly, someone thought a wee sleight-of-hand with a donation or two was in order. In any case, someone should ask the Electoral Commission to have a quick look.