Just an update:
Oil analysis by Millers showed a tiny amount of fuel. 0.2% dilution or about 18 ml! ie No issue and certainly does not account for the 200 - 300 ml increase I was experiencing.
(Interestingly, its enough to knock the oil grade from 50 weight down to 40 weight though! - Makes you appreciate that long periods with the car idling on a cold engine, or short runs will require more frequent oil changes, rather than high mileage long runs) Millers lab tech say that fuel evaporates off at a comparatively low temp. so a good hot run should get rid of a bit of this fuel contamination.
Also good news was there is very little wear contaminates present in the oil after 3,000 miles and engine is in good condition.
All back together now. One injector replaced as it was slightly down on others, otherwise no issue. Injector rails cleaned of rust and painted with POR15 to protect them, so that's one job that needed doing taken care of. - Cheers C11BRA
Oil level has dropped again!!! I think Skinny-monkey is right, and maybe simply a case of oil caught up, or not, depending on conditions.
(Also Ragpicker might be correct too!!)
Thanks again to Demort and others