I've just ordered a bundle of plants from https://plantsavers.co.uk/. They are worth a look if you don't mind a random selection of plants that would otherwise have to be ditched by nurseries because of Covid19. I'll report back when they arrive and tell you what I've got! They are delivering to London and parts of the south east at present, but may expand their delivery area if there is demand.
The plants have arrived! I ordered the perennial selection and received fifteen plants and a bag of compost for £35. The plants look in excellent condition - all decent sizes and healthy. There are three each of campanula muralis, heuchera 'Palace Purple', pulsatilla vulgaris 'Violet', gaillardia aristata and salvia 'Edula Blue'. Having looked them all up on the RHS website there is a good mix of colours and seasonal interest, and should go some way to filling my now-cleared borders. I'm really glad I took the plunge and ordered blind, as there are plants there I probably wouldn't have bought (mainly because I hadn't heard of a couple of them!).