see
https://www.landyzone.co.uk/land-rover/how-can-i-check-whether-my-td5-head-is-cracked.316656/

Stanleysteamer said:

see
https://www.landyzone.co.uk/land-rover/how-can-i-check-whether-my-td5-head-is-cracked.316656/

Click to expand...

That's a nice thead which confirms that the symptoms described by the OP are very unlkely to be caused by a cracked head... I insist that it's a fuel supply or management issue

I know you said injector seals had been done but if genuine hadn't been used I'd be getting them swapped for genuine and go from there
Mine wont start on anything other then genuine orings and seals
Might be worth lifting pump out of yank and see if its covered black soot an sure sign of combustion gases getting into fuel supply