Update #2:

There's good news, bad news and not so bad news:

The goods news: it's definitely the driveshaft (good as opposed to being the diff that's gone)
The bad news: New one is £250 from Ford!!
Not so bad news: A recon one is £240 fitted, (on an exchange basis).

I was considering getting one from ebay, but I've not got any comeback if it fails again. So gritting my teeth and paying the money. She's booked in for Friday. Don't know specifically what's happened to it yet, but I'll ask when I pick her up, and ask if I can get some photos of the old one before they exchange it.