The common thread here is that it's not our lines, access network, or transit to the UK. But Valorant itself, possibly due to how we connect to them in the UK. (Which is why other ISP's may not exhibit the same problem).
I'm now monitoring several of their servers, to establish some trends. If we can bypass a bad peeringing relationship with them we will, but it's not simple. They have servers on AWS, and also some of their own, all of which take different paths.
Again, as I always encourage gamers, insist that they at least deploy some local servers. We now have AWS, and Azure, so their excuses are running out.
I refuse to even install Valorant (being a keen FPS gamer myself). I refuse to accept 140ms pings.
Thou shalt not have my money.