Just 2 comments...
1. Why not post this on uk.rec.gardening?
2. You are going to need very heavy containers to stop them being blown
over in the wind, unless you intend to have them somewhere very sheltered.
Tree type cotoneasters,
White berried Mountain ash,
Flowering crab apple on dwarf root stock,
Various slow growing conifers
and many more, depends if your site is sheltered, close to the sea or what.
--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk