We gook the head off due to a hairline crack in combustion chamber number 3.

New head sourced and then refitted yesterday evening.
All was going well until we tried to fire the engine into life and was greeted by lots of coughing and spluttering.

On closer inspection after the comments above, one bank of the coilpack has cracked and started to distort, just bought a new one and it all magically came to life