I am loathe to pay a $8000 business class fare for IAD-LHR midweek so booked a flexible (M) economy ticket online. When I went through the process at ual.com, I was asked if I wanted to participate in a pilot offer of an upgrade on one leg to business class for $450 more.

Seems like a good offer. Anybody else try this and have any thoughts on it? Is this offered frequently if you book in M class?