Steve O'Shea;93173 said:You are a naughty lot! Magdalena is my sister!
Phil;93239 said:Oh dear, answering my own question immediately.
Yes, it probably is Titanites giganteus or Titanites anguiformis; here are more examples from the same region:
Fossils of the Portland Group - by Ian West
Oh dear, if I'd re-read the article properly I would have noted that the thing was found in limestone, not chalk. What makes it worse is that I used to visit Christchurch as I had a good friend who lived there - I should have remembered. Doh!