Representation of UK nations
For her coronation, Queen Elizabeth carried a bouquet of all white flowers, with orchids representing England and Wales, stephanotis Scotland, and carnations for Northern Ireland. The king is unlikely however to carry a bouquet, (although the Queen Consort may) so it will be more of a challenge to incorporate the UK’s national flowers. Perhaps we’ll see these appearing in arrangements in the Abbey.
As red is part of the official coronation emblem expect both red and white roses representing England. Eryngium is perfect for the Scottish thistle, with sprigs of shamrock for Northern Ireland. For Wales it is of course the daffodil, paperwhites would be ideal, and if grown on the Isles of Scilly, even better.