Starting reading some decent books. Some of the 'classics' from back in the day will show you how to talk like a proper toff, and you can tone it done for contempoary society. Also a broadsheet like the times or telegraph should help cos they're always poncing it up!

Also i'd say watch some films like the BBC's production of Pride and Predjudice. Lots of poncey phrases and stuff in there. I used to 'borrow' some when talking to my managers at my old job if they'd ever pissed me off about anything. They'd look at me like i was bit weird, but it always unsettled them to be using eloquent prases and words they weren't quite sure about.