Just an example not a final build.
CPU: AMD Ryzen 3 3100 3.6 GHz Quad-Core Processor
CPU Cooler: Cooler Master MasterLiquid Lite 120 66.7 CFM Liquid CPU Cooler
Motherboard: ASRock Fatal1ty B450 Gaming-ITX/ac Mini ITX AM4 Motherboard
Memory: Corsair Vengeance LPX 16 GB (2 x 8 GB) DDR4-3200 CL16 Memory
Storage: Crucial P2 500 GB M.2-2280 NVME Solid State Drive
Video Card: Palit GeForce GTX 1660 SUPER 6 GB StormX Video Card
Case: RAIJINTEK Metis Plus Mini ITX Tower Case
Power Supply: Silverstone SFX 450 W 80+ Bronze Certified SFX Power Supply
Total: ~£725
You've got enough budget to get a better CPU, e.g. an R5 3600, or a better cooler, or a bigger SSD. Lots of options really. I am sure there will be more people along with more opinions.