This seems like a pretty darn good deal, looking in PCPartPicker it works out at roughly RRP for everything including the GPU (others may come along with more detail).
What I would upgrade:
PSU to 750W for £19.95
RAM to 3200MHz for £9.95
Storage: this is entirely up to you, there's a steady stream of decent storage deals on HUKD.
edit: rough component adding up
CM TD500 ARGB £85
5600X lowest ever £221, currently ~£260
MSI B550M-A PRO £85
16GB DDR4 3000MHz £60 at least?
CM 550W white-rated PSU £42?
Adata SU630 240GB £27?
RTX 3060 RRP is... £300? Good luck finding one for anywhere near this though, I haven't seen any prices under £400 for a while now, usually over £500.
Plus Windows and putting it all together and the 3Y warranty, it's not a bad deal.