23:13 Nov 29, 2009 

Thanks, Jim. That is clearly what it is - I was just undecided what to put that would mean anything to English-speaking visitors to the website. I've decided to omit it. I now see that the question has been deemed "non-pro" which strikes me as a rather unthinking disposal of the question as it should have been clear that it was not a translation as such that I was after - anyone could have stuck down a literal translation. But there you have it.

13:20 Nov 29, 2009 

This is group of professionals who work together. It is half way between completely independent professionals and a partnership. I would avoid "association" which would give the idea of a trade association.

00:09 Nov 29, 2009 

Googling a number of well-known legal practices, I saw that none had any kind of descriptor after their name, other than
"Lawyers", or "Solicitors" or a variation thereof. As I said in my original question, I couldn't see the point of the easy solution of a literal translation, as that is not meaningful in English. I take Shera Lyn's point that the expression exists, but the firms I'm translating for are not limited liability companies, and in any case I am unaware of its being used on websites, letterhead etc under the firm name. Thanks to all contributors.