It does look like fossil bone, but without knowing where it was found it is very difficult to do anything other than guess at an ID. This is because the formation it is derived from determines it's age and whether it is likely to be reptilian or mammal.
Why didn't anyone teach me this in school?
Really appreciate the replies, I'll try to retrace my steps and figure out where it's from. If it's not east Norfolk cost through to Essex it's from Devon.