At Oxford and Cambridge universities, honours are not awarded to degrees but to examinations. For example, in my Engineering M.Eng course, I got a II.1 class in my Part IA examinations, a I class in Part IB and IIA, and a Distinction in Part IIB (the M.Eng examinations are not awarded honours: you can get a pass, merit or distinction). So I got two firsts and a II.1.
In Maths, the course structure is made up of the BA (three years, Parts IA, IB and II) and, if you do well enough in your BA, the M.Math (a.k.a. Part III --- this used to be called the Certificate of Advanced Study in Mathematics). You could, in principle, get up to four firsts in Mathematics.