Whoever/whatever Russia favours and chooses to fund tells you precisely who/what would strategically weaken the UK the most. Brexit is a prime example.
It's not that the right has been bought or infiltrated by Russia, or that it somehow aligns with Russia ideologically.
It's literally that the Russian administration has identified the right as UK's biggest economic and political liability, and wants to invest in us fucking ourselves over.
If it has worked for them so spectacularly in the US with Trump weakening America, why wouldn't they try doing it to us? A few million in donations here and there is absolute peanuts for the potential strategic impact.