you can either just buy the head gasket or buy a full top end gasket kit but make sure you have the cylinder head skimmed and pressure tested just to make sure the head is not warped or cracked or you could end up just wasting time and money.
I have just found some really good guys in Reading, Berks for engine machining etc - PM me for details. The do leak testing, skimming, valves, rebores, top hats - the whole caboodle in house. They also do engine ecu remaps and dyno setting up.
some people are saying you shouldnt skim a td5 head and some say a "light" skim but i would check with someone who is 100% sure. it sounds like the tolerances are very fine.