Plebb - someone who's not too bright and maybe a bit out of touch with fashion etc.
Clanger - "dropped a clanger" is a phrase used a lot here
e.g. - A friend of mine congratulated a collegue when she thought she was pregnant. But she was shocked when the collegue said "I'm not pregnant at all, i've just put on a bit of weight". That's an example of "dropping a clanger"
Plonker - you often call someone this if they've dropped a clanger. It's also slang for male genitals
Divvee - sporned, I think from Liverpool and best said with a broad Scouser accent (that's what we call Liverpudlians) Just "Div" is used sometimes.
Lard Arse - someone who has a big backside and is generally overweight
Tosser - someone you don't like but also the same as "wanker"
Dickhead - again someone you don't like (this theme goes on .. Prick, Prickhead etc)
Dweeb - very much like Plebb above
Scum - Someone who'd rob your grandma or any other crime of that ilk
Arsehole - I think this is one of yours too, but maybe you say "Asshole"!
Sporned - to grow or develop
Country bumpkin - someone who lives in the countryside, away from the city
Pyscho - someone with a screw loose - they'd do anything and are best avoided. I guess sporned from that great film.
Headcase - as above, but they're probably not as dangerous.
Daft prick - [note: Kev didn't provide a definition for this one; it's self-explanatory.]
Sod off - piss off
Sod - someone who's a bit of a runt and a bit canny is often described as a "sod"
e.g. - "that little sod's borrowed my car without asking"
Clown: an idiot, fool
Nonce: Someone who's feeble minded and probably on the camp side