Check the base of the plant to see if there's any new growth - the problem is probably to do with the sudden arctic temperatures during February after a winter that was more like an extended autumn. Hopefully the roots are still okay and you might find new growth comes up from those rather than off any topgrowth still present. Might be wise to cut it down, checking as you go whether the stems become 'live' near the base or not.

I'm afraid you are not the only one. Mine did that last year. It did have new growth from the base but it took a lot of time to get going and no flowers. Problem is that it's done the same again this year so I've pulled it out, it just wasn't the right spot for it obviously. Yours sounds like it had been doing alright so I would be optimistic, but the growth will probably be from the base and will take time.

Bamboo,
Thanks and I have now checked more thoroughly. I find there are some green leaves behind the brown ones so it will recover but I expect it will take months.
I can't face cutting it down/back! The roots will be o.k as they are well protected and probably quite deep.
Linmar