Hi all,
Sorry, this isn't going to be much help - can't find Jacob under either name in 1841 - but just thought I'd mention that there's a criminal register for a Jacob mentioning an alias.
26 Jun 1843 Durham
Jacob Salkeld also Saville, Degree of instruction Imp, age 26, larceny, before convicted of felony - sentence 12 months
Not sure whether this is the previous conviction:
5 Jul 1839 Northumberland
Jacob Saville, Degree of instruction N, age 23, Larceny - sentence 6 months