I'm convinced it would survive in sheltered Cornish gardens because it has dipped below zero in my greenhouse on occasion, but moreso because the many stems which have crept out of the greenhouse have been completely untouched by all of the (often quite severe) frosts over the past decade.
I read that it tends to flower on more mature wood so I have been trimming the whippy bits off, rather as you do with Wisteria, until the main stems are about a centimetre thick.
Only the one bunch so far but it's a start and hopefully and indication that the plant is mature enough now to start blooming more regularly and heavily.

