OID description:
The ISO member body for Great Britain (GB).
The rules for this OID arc are given in British Standard BS 7453 Part 1 - "UK registration for Open System Standards - Procedures for the UK Name Registration Authority".
Section 4.1.5 subsection a assigns the arc {iso member-body gb(826) national(0)} to the UK Name Registration Authority, and subsection b assigns "the object identifiers distinguished names of localities, each formed by concatenating as a prefix the object identifier/distinguished name from 4.1.4 with one of the sequences of (object identifier component/relative distinguished name) values assigned to localities by the Registration Authority".
So if it starts with a zero, it's a national name, if it doesn't, it is a regional name.
The UK has also chosen to limit OID component values to the range 1 to 2^24-1 (16,777,216). The omission of zero either indicates that they made a mistake or that zero is reserved for the registration authority.
See also the OID Repository website reference for 1.2.826