For any passenger flying on international executive first (or for SEs, flying in either cabin), one can access to a concierge. In my case, when we flew to Edinburgh via YOW and YUL and LHR in July 2004, we were met by the concierge on arrival at LHR. He facilitated the three of us in reaching the arrivals lounge quite quickly (even with our privilege of being able to use the immigration line for business class passengers - the concierge was able to save us additional time with these formalities), and indicated when we should leave the arrival lounge for the the BMI checkin counter (the AC checkin agents in Canada were not able to issue the BMI boarding passes at that time - I do not know if things have changed now).

If one wants direct lounge access without worrying about going to the arrivals lounge, one can go airside from T3 to T2 (YOW KID, am I right?), and reach a BMI lounge. However, the 3 things the AC arrivals lounge had, which I could not find in the BMI lounge, were showers, free local phone service, and a computer.