So its after lunch now and still no call, so I think we can assume he's going to retain his anonimity for a while longer since it allows him to continue with his free parking.
Landlord has got back to me and basically wants nothing to do with it, considers it a matter to be resolved between tenants. A point I would agree with if I could speak to the chap.
So, if he's there tonight I have a solution, a collegue from the university lives in the next street and is happy to park his car behind the Hyundai which of course will block him in (shame). That should force him to contact me and I won't let him out till he tells me where he lives.
Hopefully the situation can still be resolved in a reasonable way.