Whereabouts in the UK do you live Robin (city or county, not your whole address). I understand that Ceanothus is not incredibly hardy.....

'Yankee Point' is a ground cover, not a tree! Is this grafted onto a trunk to form a weeping standard, Robin? If so, you will need to take pains to protect the trunk during the winter.

Interesting - I looked up Yankee Point on Shoot - there it says height and spread 8m! But my gardening bible says height after 2 years max 2 m, spread 7 m. Burncoose says height 1m, so take your pick. I'd go with the 1-2 metre height with a 7 metre spread and add the length of standard stem to those measurements.
I also wouldn't plant those myself now - best planted in Spring, when the worst of winter is over, so if they're still in pots, I'd keep somewhere very, very sheltered with the pots wrapped in bubblewrap, clustered together.