A bit late to be replying, but anyway... I can't answer why Septimus was in jail in 1851, but I did come across an account on Ancestry about an affray in 1877 that has an interesting connection. Together with my great-(n)-uncle Anthony Jacques, one Septimus Bland assaulted a police sergeant and several others at Quarry Street, in front of Jowsey's beerhouse, Shildon. I don't have a paid membership to Ancestry, and probably can't provide a link to it that would work, and I think it a bad idea to just copy and paste the whole thing here in deference to the no-doubt crack team of lawyers Ancestry employs, but hopefully I've given enough info that you could find it yourself if you do have access to Ancestry.
On the 1881 Census I note that a Septimus Bland (born 1812) and another (born 1857, year before my relative Anthony Jacques) were living together in Whitworth, which is also in the same area. I speculate that Septimus the elder is the one you're looking for, while the younger is the one getting into trouble in 1877. Presumably having legal problems ran in the family (or was a consequence of poverty etc).
