Thanks for the speedy reply Ian.
As of yet no the injector has not been replaced, would one failing injector be sufficient to completely dissipate rail pressure generation?

I am reluctant to now put an injector in until I'm sure it is that causing the starting issue as that is the customer complaint, not the driveability issue.

As I said there is no obvious misfire so the injector is still functional to a point. Maybe I should try disconnecting the one injector before starting to see if rail pressure increases more efficiently?