I have no idea what a 'weak interruption' is; it does not sound like a grammar term. Royal bank of Scotland was the first bank to sign up-- Main clause announcing last month that it would ask the government to insure £325bn worth of so-called toxic assets, which are difficult to value and currently cannot be sold -- adverbial dependent clause modifying the main clause. which are difficult to value and currently cannot be sold-- non-restrictive dependent clause modifying '(toxic) assets'.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.