Peter, I struggle with this all the time. A federal deputy in Brazil is equivalent to a US Congressman. But only in the more informal translations would I translate it this way. I end up using federal deputy with the nagging feeling that the reader won't know what is meant. It depends on whether the meaning is clear from context, and on who the target audience is, but you might find a way to slip in "member of the federal Chamber of Deputies." As for "representative" - if you are going to go straight ahead with the US term, I find Congressman clearer. There are some people who regularly translate Chamber of Deputies as Brazilian House of Representatives, but I think that's going too far. That kind of thing could go in a footnote, but in all but sensitive texts I avoid footnotes like the plague

This answer reflects my own ambiguity, even after 25 years as a translator of this stuff!

--------------------------------------------------
Note added at 48 mins (2007-03-27 12:34:45 GMT)
--------------------------------------------------

OOPs, Peter, as usual I forgot to read the question thoroughly, you want a UK term but my answer still applies - it's better to stick with the Brazilian term, particularly if you can slip in the name of the body - Chamber of Deputies. You probably should not Anglicize any more than you should Americanize.