Spacedonkey
You'll find loads of universities that offer Italian and Linguistics. Depends where you are based, though. Do you need to be in London?
The good thing with Italian is that, wherever you apply, you'll be able to start it from scratch. Because it's rarely taught in schools Italian departments always accept beginners, and in fact normally up to 75% of their students don't have an Italian A'Level before starting their degree. It is also the case that people who start as beginners do just as well as (if not better than) the ones who started out with A'level by the time it gets to their final exams.
AFAIK, you'd be able to combine Italian with Linguistics in most places. Again, because Italian tends to be a small subject area, combined degrees are very common.
I have taught a huge number of mature students (oh yes, that's another good thing about Italian - attracts a large number of mature students... probably precisely because of the fact that you can take it from scratch). In recent years more and more of them have done access courses, and they do seem quite well-prepared by them. In particular, if you've been out of education for a while, the study-skills elements seem very useful. I don't think an Italian department would mind what subject area it was in... not sure about Linguistics departments. Some Italian departments would want to see some proof of an ability to learn a language - e.g. a GCSE or equivalent in any modern foreign language or Latin. However, a lot would waive that criterion if they liked the sound of you.
Most combined degrees with a modern foreign language will require you to spend a year abroad. Not sure if this is a problem with kids (shouldn't be - I've seen people simply up sticks and take their kids abroad with them) but obviously it is for some people. Some language departments are now introducing 3-year versions of combined degrees without the year abroad, so if this is an issue it's worth shopping around.
Hope this helps. In bocca al lupo!