Having looked it up in the UK I think you have the answer, it IS Mrs Robert Bryden.
Growing where it was on a south facing wall in a very sheltered, South of England it could be evergreen in milder winters and our last 10 were. This winter may well have been rather different, its been the coldest for over 30 years and a couple of mine that had been evergreen the last 3 years I thought had actually died completely. I'm relieved to see basal shoots re-appearing on one so fingers crossed for the other.
Even the tough old Montana is still thinking about whether or not to grow - but that does have the coldest and draughtiest spot in the garden, deliberately planted to block the draught through where one of the evergreen trees had died some years ago leaving a convenient branched pole.
I shall now go looking for Mrs RB. Thank-you!!
