Calif has very strict laws about letting any kinds of plants into this state,even if you are here in the states,and come to calif,you're subject to search and seizure,and they don't care what it cost you,or where it came from.

Unless it's change over the last few years,this is how it was when we traveled to the east coast etc.

I'm sure someone here has been in and out of the country more recently and may have more updated info.
Kathi

It is better(easier)to have the UK nursery ship it to your home. They know what is required and have the license to do it. California spends millions eradicating pests that have been brought home by travelers overseas. Al

A few years ago I brought back, from my daughter's garden in Oregon, a small plastic bag of dirt with 4 or 5 lily of the valley plants in it.
It set off the alarms in the Portland airport and they took it far away from me and searched for the cause. Not finding a cause they gave it back to me (!!!) and when I was planting it, I found a 2" rock in the dirt that they had missed.
Through all this, no one said a word about importing a plant to California. (Or a radioactive rock- HA!) Min