Got home a few hours ago. DS went out to Welcome Party last night. Didn't divulge any info - had to be tied down and interrogated before we found anything out!
We took him to Sainsburys and £100 (and a faint!) later, we offloaded him back at halls and said G'bye.
So, that's it; it is done!
I was a bit choked as we left but managed to hide it. DH was a bit miffed with him when we left as his attitude was rather disdainful. 
He says he's coming home at the end of Oct - we probably won't hear from him until he needs a lift, unless he runs out of cash beforehand! 
So now my attention turns to DS2 in Yr12... 