Lady Northcliffe, (and as Christopher Lloyd writes in his excellent and still very current book on clematis, ‘not Northcliff, (the sort of cliff that faces north)’.
Also from Christopher Lloyd in his book, updated by Tom Bennett, 1989, writing on blue clematis:
‘The deeper blue shades are more popular than the light. Here our choice lies between four old and well tried varieties: ‘Lasurstern’, ‘Lady Northcliffe’, ‘Lord Neville’, and ‘Beauty of Worcester’.
Lady Northcliffe has much the same colouring (..as Lasursturn) and is as good it its way, though I have seen it afflicted with mildew. The flower is quite a different shape, without fine tapering of the sepals and unwaved, but the bloom as a whole has a classic purity of outline that is characteristic and always recognizable once recognized. This clematis was raised by Jackman’s from a cross between ‘Beauty of Worcester’ and ‘Otto Froebel’. It received the AM when shown by Jackman’s, 29th May 1906.’