Update:
I eventually ordered all three birth certificates that were showing a mother's maiden name of Jones. The first two were incorrect (wrong father christian name). The last one I received showed a Jane Roberts, born on 7th January 1855. Father William Roberts, a Seaman Merchant Service, not a Labourer as shown on the marriage certificate of Jane. The mother is listed as being Jane Roberts, formerly Jones. I have based the search on the years 1853, 1854 and 1855 as her death certificate states that she was 61 when she died on 28th January 1916.
I found this family in 1851, 1871, 1881, 1891 and 1901. William was listed in occupations Mariner in 1851 and Fisherman thereafter.
It looks likely that Jane's mother may not have been a Jones after all.
Back to the drawing board.