what phone would you recommend for under £500/400Watch
This, OnePlus phones are better than many that are twice the price. They have an AMOLED screen so you can hide the notch completely if you don't like the look of it.
It has all of the internals of a phone for £800+. There's no bloatware installed at all unlike Samsung. The dash charge thing they talk about is insanely good, probably the best fast charging available, the phone doesn't heat up at all while it's charging and it charges from 30% to 95% in the time it takes me to get a shower in the morning.
The only thing you are missing is wireless charging but you really don't need it on a device that charges from 0% to 100% in like 45 minutes.
Their customer service is really good too, especially for a less well-known company. My OnePlus 3t had a small issue with the touch screen after I had it for a year or so and they fixed it for completely free in about a week, no shipping costs or anything, and sent me updates on the progress in the meanwhile. (also they replaced the panel with the one from a OnePlus 5 which is slightly better so I basically got an upgrade)
You can also get them from O2 if you don't want to order directly from the factory
If you want to go really cheap you can get a used 3t on ebay for like £200. I got mine on release and it still holds up well I haven't thought of getting a new one yet, Just inspect the images carefully so you only buy one that has been taken care of. I'm really wary of buying used electronics because I know people would just try to sell something when it stops working properly.