Rareplants.eu emailed an update to the situation this morning, stating that the requirement for a phyto' has been postponed again.
I have flicked through various links, including some on the DEFRA website but can't find any statement beyond ones that suggest that the postponement is in place until the requirement is introduced.
Whether there is a reciprocal state of affairs, I have no idea.
I did have a small padded envelope of seeds opened by Plant Health recently, presumably to check that no banned species were included? That had come from Germany.