Just wanted to get back to you all and confirm that with your help we now have a running and reliable car
It turns out that rather than being a single problem there were actually multiple problems some of which look to have been caused by a previous "enthusiastic" owners maintenance. The root cause of the issue was an intermittent connection between the ecu and the negative supply to the injectors, however following all of the advice on this site I also found the main fuel pump pressure was not up to scratch so also replaced that.
The error messages found on the diagnostic were traced to yet another wiring fault which i have also now resolved.
Ultimately i do not think the car has run this well for years! I just have to finish setting up the throttle body and tick over (my timing light with RPM indicator is on loan to a friend) as it feels a little too low.
Once again I appreciate everyone's help and hope i can return the favour with some of my new found Volvo knowledge.