Thanks, I realise there is no business class on UK Domestic. As mentioned in previous posts, the passenger has flown this exact itinerary on numerous occasions in the past, each time on the same 'I' class fare, and each time has had no issues gaining lounge access on this kind of ticket, hence why I started this thread.

The ticket was purchased by his employer, so perhaps they have negotiated a corporate 'I' class fare with the theoretical flexibility of 'business class', but without some of the bells and whistles attached. As sunrisegirl suggests, perhaps he has simply been fortunate on previous occasions.

For what it's worth, the flights always post as full miles and TPs, so I guess not all is lost.