I'm not from the UK, so I don't have a deep understanding of the dynamics of politics there, but it seems like avoiding all situations where even the suggestion of impropriety is impractical for just about everybody who might be in a position to be PM.

If you're in a position of power, you're going to have relationships where there might be the appearance of impropriety for anything - and you may not even know there would be the suggestion of impropriety until after the fact.

Infosys has 40 clients w/ greater than $100m/year contracts, which they don't enumerate individually, but from skimming the internet, it looks like oil and gas, banking, manufacturing, and tech companies all potentially fit into that bucket - so should he recuse himself from everything that is related to any of those industries?

Before he was married into Infosys, he was a banker and presumably has lots of relationships with these large companies regardless - should he recuse himself from anything that might touch any of those large companies? Not a rhetorical question, I'm trying to understand what the criteria is.