Splitting domestic and international makes sense. Purely from the perspective of individuals and managing their own affairs
Farage would fall into international though under any definition though a) because he was an MEP rather than MP b) he has worked in and has close associations with the US and us political parties c) the Russian connection and the Belize connection are hard to ignore as this is where he has received considerable known funding either directly or through his closest associates and this is public knowledge.
In terms of being classified as domestic that would encourage to keep all your income domestic. Which isn't that hard imho. If you are an MP what reasons do you have to have an income from overseas if you are employed and paid by the state?
If you have additional incomes this immediately constitutes declarations of interests and always potentially poses a conflict of interest. That's why secondary incomes are ALWAYS potentially problematic in politics. You HAVE to be squeaky clean.
Farage has never even attempted the squeaky clean approach. He has offshore interests which he has admitted. He has done foreign political rallies. There is no way he escapes.
All high profile political figures should be scruntinised and questioned in terms of their business and associates as a matter of standard practice. This is the cornerstone of democracy.
When he declared himself the lifelong leader of the Reform Party that really showed him up in terms of his ideas on democracy and disrespect for the views of others. It was a vehicle for pushing Brand Farage and Farage's own political interests. It was an overreach in a many ways.