Originally Posted by travellingblade

In my experience they are offered when all the following conditions are met:

1. There is I class availability;
2. There are no domestic legs in the booking;
3. All legs in the booking are on BA metal;
4. The ticket was booked on ba.com (not including ba holidays);
5. LHR or LGW must be the first and/or last destination in the booking (so XXX-LON is ok as is LON-XXX or LON-XXX-LON, but XXX-LON-YYY is not)