Hello Kev, and fellow posters;
It is very interesting to read others experiences, good and bad, of using engine flush; I have always flushed my engines when doing an oil change, something I do at least four times a year, but always use the following method: run engine until warm, drive hard until very hot, add flush, 5-10 minutes at idle, drain whilst scalding hot, then leave jacked up overnight, or longer. Refill with new oil/ new filter. Idle for 10 minutes, let stand, check levels, adjust as necessary, run again, recheck, job done. Normally for the next week, checking the oil level is tricky as it is so clear!
Kev, best to call Nigel on 01884 855373; I know they will visit you, but don't know their charges for this, but if you go to them their website is running a special price! Oh, and the injector cleaner is a good idea, but I believe some brands will also attack the copper seals which will hardly improve things, if they are past their best...!
Best of luck, and don't forget to update when you get to the bottom of it!