I just got an email from the Google Webmaster blog saying that Google have launched a change to their ranking algorithm that they say will make it much easier for users to find a large number of results from a single site.
For queries that indicate a strong user interest in a particular domain, like "exhibitions at amnh" (The AMH is the American Museum of Natural History for us Brits), they will now show more results from the relevant site, as shown in the screenshot below.
Not quite sure at this point whether this really means anything for UK law firms, so we'll have to wait a while and monitor things.