Solved!
I can confirm that I have fixed the issue with the car losing power as per first post.
It looks as though a previous owner has attempted to fix the issue with the N/S intercooler hose pushing out and in turn fitted the incorrect spring clip, giving my answer to the post above this one!
The incorrect clip fitted was a 1J0145769G; I have now replaced which the correct clip as fitted to the O/S hose 1J0145769H. For good measure I also cable tied both O/S and N/S hoses to the intercooler to prevent any leakage as the ally lugs wear down on the hoses.
The result... took the car out for a blast and it pulls hard through the revs in every gear with no hesitation! Check the intercooler hose again and lo and behold, there it is still fitted snug into the intercooler with no more oil vapour leaking onto the undertray.