What HiFi and Techradar websites are always useful pointers. The later has already published an article about Amazon's prices for their devices on their US website and that it's a good indicator of the deals that can be expected in the UK.
This ^^
Just picked up two iPhone XRs for £329 each after an O2 deal appearing on there. Lots of stuff pops up on there but it is a lot to go through unless you know what you are looking for.