Shouldn't be too difficult. The Wikimedia UK site does not appear to be a wiki curiously enough, so it may be easier to start the relevant pages from scratch. There's also a ton of stuff on Meta-wiki that can be imported.
There is very little on the old WMUK site that is about the new chapter. Most of the stuff that needs to be transferred to a new site is the stuff on meta, the old site just needs to be redirected.