Thank-you for all these replies; I have just got back from a day out, and am trying to take in the wealth of information. William Cook(e)'s parents were Thomas and Elizabeth, and he was a coal miner. In 1851 he was living at Newbold Moor; in 1861, Alsop's Place, Newbold; in 1871, 7 Alsop's Houses; and 1881, 7 Alsop's Row. He probably died 1882. His status is given as married throughout, and he did not marry Rebecca Thorley, with whom he had a daughter in 1871, as she married another miner in 1875. The Caroline Bostock/Cook/Spotswood you have traced looks a strong candidate for the missing wife. I had guessed that the missing wife was in an institution, as William continues to describe himself as married; if Caroline did marry John Spotswood, it must have been bigamous, though perhaps William did not know about this. I clearly need to have a good look at the censuses and then order some certificates. I keep writing up chunks of family history, but it appears that this branch of the family needs a novelist rather than an amateur historian!
Anyway, many thanks for your help. If you have the interest/energy to come up with any more information, please do; and if you can use your experience to come up with better interpretations than mine, then again I would love to hear them.
Repeated thanks
JohnE