I've just had a reply fro the InterContinental Ambassador Service Centre.

They assure me that "Ambassador members are entitled to an upgrade to a room one category higher than what they have originally booked."

They also say, and this answers the question about how they guarantee an upgrade, "InterContinental Hotels & Resorts properties upgrade the member's room once the reservation has reflected on the hotel system."

It would appear, therefore, that although you don't get the upgrade until check-in it is actually booked on the system prior to this. They have indicated the upgrades I will get at both of my pending booking.

So, anyone who is fobbed off with a "room with a view" or "better location" upgrade, argue your case! Unless of course that room is a room one category higher than what you originally booked .