I think ryzen 7 or i7 is worth shooting for, if you guys agree and think so too, my son would be happy I am sure, and a 4080 looks a great card.
If you're getting a card like the 4080 (or anything around that kind of performance level, including the 5080 and 7900 XTX), I'd normally have the 7800X3D or 9800X3D in the spec.
The 9700X is a step down on the X3D CPUs, but still performs very well.
It being a Ryzen 7 isn't necessarily an advantage, most games still run perfectly fine with 6 cores, but the X3D's cache is a big bonus and the 9700X has good single thread performance and high clocks. Getting a 7600 or 9600 would truthfully be indistinguishable with the 7700X/9700X in a lot of games, it is just that when you're forking out £1K+ for a graphics card, does it really make sense to limit it with a £200 CPU?
The i7 is a difficult one. The 12600K is something I only suggest because of the price, since with a DDR4 build it can undercut the AM5 options. The 12700K is a nice CPU, but as a gamer, the i5 K CPUs are more than capable and the i7/i9 CPUs offer the greatest benefit in productivity (due to the increase in P and E core counts). For that reason, it is hard to recommend, especially if paying nearly £100 extra, though you can often get the 12700KF pretty cheap.
The 13th-14th gen i7 CPUs are potentially problematic, there are a few on other forums who had to RMA their CPU twice. You do get an extended warranty on retail boxed CPUs, but for a gamer I don't see the point taking that gamble when you can just go AM5.
You could get a 265K instead, which is problem free (so far as we know), but like the 13th-14th gen i7 CPUs, this is mainly competitive in productivity and in some cases it performs slower in games than the CPUs it replaced (with decent memory and all the patches, they're definitely performing better than they did on release day).
With the 4080 specifically, are you looking at used cards? Personally, for 1440p, I'd try and get a 9070 as close to £500 as possible. It'd have more than enough performance for a good few years and won't break the bank. Unfortunately that's a tough ask right now.