Mine too Margot (3 of them). Haven't given up yet but no sign of new growth. I shall just leave them for about 6 weeks (I remember they were quite slow in kicking in from last year). I love them but if they don't come back I shall replace them all with clematis which are also great and mine all survived after the horrific winter.

The one on my side of the fence (quite old, with a 2inch thick stem) looks a lot like it's died. But the young plant (seedling off mine) on my neighbours side of the same fence it just showing tiny growth buds. It's still early for these to start to grow, but keep an eye out with this warm weather. I hope it has survived.