Well, I live in New York and I have this very same flower - I just posted a picture of it yesterday. They are at least 20 years old. It can be trained into a shrub, tree or hedge.

http://www.growsonyou.com/photo/slideshow/333033-rose-of-sharon/member/bathgate

I don't know how many blizzards, hurricanes, tornadoes, earthquakes, droughts & hail storms they've been through but are not phased by any of it. They bloom reliably every years. I also have a blue one. Here it's called 'Rose of Sharon' and it's just a hardy hibiscus. Mines are planted in the ground and they are fully hardy.

Hi, welcome to GoY, 'woodbridge' is a cultivar of H syriacus, and is fully hardy, grow it in full sun, in humus rich moist but well drained, neutral to slightly alkaline soil, Hibiscus need a long hot summer to flower well, Derek.

Yep, a sunny southern is recommended in the UK.