Look like the back of a bus

I'm trying to find the origins of the saying 'look like the back of a bus'.

Could you help, or point me in the right direction?

Referring to being broad in the behind department?

No, it's a British phrase just meaning "ugly", with no particular connotation of stoutness; it's at least half a century old, and so well known in the UK that there are jocular variants such as "like the north end of a southbound bus" (VSD)