Hi Lindsell,
Thanks for your offer. I now have copies of the two birth certificates in question (actually, I don't have them, because at the time of the original query, I was in the process of moving from Canada to Thailand, and so had "no fixed address" - so I ordered the certificates to be sent to a cousin - he has them, and has reported the details!).
Anyway .... the girl, Mary Jane Noble, was born 16/1/1857, as her age in the 1871 census suggested she might be, but her birthplace is given as Christiania, not Leeds as per the census record. Her brother, Robert Noble, was born 16/1/1859, also in Christiania. Strangely, both were registered on the same day, 16/1/1860 (just a coincidence that this was Robert's 1st birthday, I wonder?). As I understand it, Christiania is a district of Copenhagen, from where the British Consulate covered British affairs in Norway. But Robert's birth in subsequent censuses is "Norway". It seems the listed birthplace must have just been some bureaucratically convenient fiction!
Unfortunately, these overseas certificates provide no address for the parents, so I have no way of knowing where the family was actually living, though seemingly, in Norway.
Also strange is the fact that in the 1851 and 1871 censuses, the father, William Noble, was a manager of a mill. I had gathered from some internet research that in the mid-19th century there were efforts to develop a textile industry in Norway, so I'd assumed that he had been "posted" overseas to help set up a mill. However, on the birth certificates his occupation is "ropemaker"!!
So, as far as I can see, I'm at a dead-end, because there seems to be little hope of finding where they were actually living in the late 1850's/early 1860's - unless there was a Norwegian census in which they might appear - but it would need to be indexed by name!
Thanks again for your kind offer, but unless you can discenr something I've overlooked or misinterpreted, I don't think I can take this further.
Cheers
Tim