I had the head checked/skimmed and valves and seats re-cut (Engine services in Leicester for £80), the car is now back together and running well again.
All in my 406 has recently had a re-con turbo (shaft bearing spun and blocked oil way on old one), new water pump, timing belt and pulleys, a re-con high pressure fuel pump plus the head work already mentioned. Luckily I was able to do all the spanner work myself so saved a lot of cash there, maybe if I had to pay somebody for the labour costs the old girl would have had to go
If anyone ever does this job and shears half of the torx head off of a head bolt as I did
I have made a two piece guide tool for drilling and milling the rest of the bolt head off in-situ and you are welcome to use it 
Thanks for all the advice and help again folks, Paul.