First of all, thanks for the feedback on the issue.
@Blunder
I am positive that at idle there is no smoke coming out of the oil cap. However after longer trip the cap is steaming, rather than smoking. I would imagine once at operational temp and longer trip this would be expected though?
The inside of valve cover seems to covered in cack/oil as looking through oil filler cap - may be just deposits accumulated over 90k miles or in fact proof of some seal/gasket problem.
The inlet manifold is coming off again-first to check how much crap is in it after 400 miles, second of all to check the PCV valve- shame i have not done it before as it took me half a day to take off and clean the inlet manifold last time

I wish i had spare £400 quid and replace that silly plastic inlet manifold with proper item of Burton Power

More compact, more power and easier to work around
If PCV valve stuck open then that would quite easily explain loss of oil... Somehow though i know i am not going to be that 'lucky'

As the PCV valve is getting replaced for brand spanking new the system is also getting Oil catch can in line so to truly appreciate how much gunk is coming out of PCV valve over time- will report on it when time comes.
There are NO obvious leaks anywhere, including gearbox area. I think i have checked all possible leak points: Crank seal, sump plug, oil filter, valve cover, head gasket area, engine in general.
I have had a Cougar V6 with oil leak around crank seal and i know how the engine bay looks like when there is oil seeping through seals- it is not clean to say at least

Mine is SPOTLESS.
@Richard G
I am not afraid of numbers and maths so could you kindly clarify how you calculate PSI knowing the compression ratio, please?
As there was not feedback to my last post for long time i have done extensive research on the topic all over internet. I have found similar statements to yours so i guess that fills me with a bit of confidence the piston rings are OK apart from teh fact they may be sticking and passing some oil due to millage on the engine - 90k.
90k is not a lot but if person before me was not looking after car properly than anything is possible...
The spark plugs are relatively brand new- 3 months old.
Fitted correctly and tightened to correct torque etc.
I am planning to service injectors as soon as i stop the oil leak. After that will replace the spark and see what happens...
Things to do next:
1. Get full gasket set. Replace valve cover gaskets.
2. Build valve spring compressor and replace all valve stem seals with head still in place. Asses the condition of valve train.
3. Get Engine Cleaner and flush engine. Get petrol additive and flash whole petrol delivery system.
4. Replace engine oil with 5w-40. Same viscosity when cold but denser when hot to slow down leaks past rings.
5. Replace PCV valve + install oil catch can.
I am off for business trip for two weeks but will update on progress as soon as i am back!
Regards.