Hi Winston
I think you've found where my Mary Foster went to.

Certainly fits with the reast of what I have at the moment. Thanks for your help.
However, I also think you've also uncovered another mystery, and that's who is their next-door neighbour, Thomas Scatchard? On the 1851 census, there's a 20 year old rope maker Thomas Scatchard, a "cousin" , living with Andrew and Mary Foster in Leeds, but does cousin mean cousin as we would have it today? Then, in 1861, the next door neighbour of Mary Mills is Jane Scatchard, 71 years old and head of household but unmarried, and living with her is Thomas Scatchard, a nephew, age 31 and a rope maker. But does nephew mean Jane's sibling's son?
Then, in 1891, Mary Foster is living with her son-in-law George Anderson and her daughter Alice in Ripon. Lo and behold, there is a 20 year old Thomas Scatchard as a boarder, not a rope maker this time, but a railway porter. That, methinks, is all a bit too much of a coincidence???
David