Managed to do the continuity test on the injector plugs to the electrical box and all was fine, typical.
Did not find the fuel pressure switch like this one https://www.famousfour.co.uk/new_parts/ff_part?part=17778, the only connection to the injectors all four of them go in to one square connection block, in the electrical box (as I call it)
It only misfires when doing 60-70mph on a motorway, bit hard to test at that speed lol. Still where the small plastic clip on the injector has broken off (left one as you look at the engine) I have re-done the cable tie and added an additional one, just to rule that out in the hope that will solve the issue. I will find out next time we use it on a motorway - fingers crossed.