I changed the wording of my answer - sounded too abrupt!
I was talking about the B550 and the OP already put the B450 Gaming Plus in their tentative build list - I only pointed out instead of paying over £90 for one,they could pay nearly £70 for it.
The issue here,is if say you could spend the £50 extra and get a Ryzen 7 over a Ryzen 5,it might be worth considering a B450 in that case,but ATM the cheapest I can find a Ryzen 7 3700X is closer to £260. I am quite happy I got mine for just under £220 due to a damaged box.
Also I do wonder with CES near,will AMD announce a Ryzen 5 5600 non-X and Ryzen 7 5700X??