I wish to thank Ticker and Wobbly for their replies. Sorry about the delay in replying, but was in the UK for December and have only just returned.
I have some more information on Harriet, but she died quite young. She married Henry Rivett, a draper from Gainsborough, Lincolnshire in 1854 in Sculcoates. She died 1869, Hull and he in Sculcoates 1876. He is on the 1871 census living Whitefriars Gate, Hull.
Wobbly was correct in thinking that my Askams were those he found in 1861. In fact the line of John Fairburn (Mibron?) Askam is the one I am tracing and have followed it through to today. The main reason I am trying to find Harriet in 1851 is that I'm hoping she will be with her parents and I can find out something more about them.
In 1841, the parents and the 4 children were living in Market Place, Hull. The father, John Askam was a grocer.
In 1851, only John Fairburn Askam (the son) and his sister Emma Fairburn Askam were living at Market Place. The son is now the grocer. I have no idea where the rest were or if, apart from Harriet, they were dead or alive. Emma went on to marry the grocer from Dewsbury.
My hope is one day to find Harriet in 1851, either with her parent(s) or with other relatives which would point me in the right direction. Thank you for your help and interest and if you have any suggestions I would be most grateful.
Best wishes,
Belen