£1500 is a decent budget - a rig with a 3070 would be a fantastic entry point and it'll already get you ahead of the PS5 for the entire generation. This could handle 1440p like butter and would be great for 4K gaming for years to come. Trouble is you'd probably need another £500 on the side for peripherals and a monitor.
If you aim to spend £1000 on the device and £500 on the side, you'll probably restrict yourself to 2K gaming and then have a pricey upgrade route going forward if you wish. It will be perfectly satisfactory though and still offer a great gaming experience but for just a few hundred more, you could literally put yourself in the high-end gaming bracket and get the best out of what is technically possible.
It's a great time right now to be getting a new PC and there are some excellent pre-built devices available in the UK at exceptional prices. 2K would offer the best value and see you comfortable for many years and with a 3070, you'd get all the extra visual effects. 4K would be more demanding as time wears on but right now, a card like that should be comfortable at maxing out games at 60fps.