If your budget is £800-1000 right now I would probably leave it for the time being. For around £1400 you will likely be able to land a high-end 1440p build that could easily support 4K when 3070's are back in stock. Where you are positioned right now, it's like having £250 at hand and then toying with buying a PS4 Slim when the PS5 is out but you can't quite afford that - it's just not viable or worth spending that money on especially for just a bit more you can get something that will keep you going for 5-7 years rather than getting something dated right off the bat. A £1000 1440p build could probably play most pre-2018 titles to a decent standard but you give yourself no scope moving forward and every new release will be a strain. Within 2 years you'll have to buy an entirely new device or downgrade to 1080p to maintain a satisfactory experience as upgrading would replace everything in the system.
If you opt for 1080p, you'll need a new monitor as your current one will make things intolerably blurry so that would be a further cost. I'd definitely see if you can scrape together some extra funds over the course of the year and once the GPU's get restocked, the market should settle down.