I've previously read on the diesel section of mg-rover.org that when a timing belt goes it usually lunches the head by smashing the lifters. The bottom ends are pretty bomb-proof. Another head assembly should see you right (like this one:
http://www.ebay.co.uk/itm/Rover-25-M...#ht_1275wt_813)
...and a Haynes manual is good enough to walk you though the process. The most tricky bit is timing the fuel pump as the instructions in the Haynes are wrong.
At least ZRed's ZR TD offer could get you out of the immediate hole, then you can review your most cost effective option to get up and running again.