Originally Posted by
MSPeconomist
Do those upgrades require availability of upgrade inventory or just an empty seat in CE (effectively that BA be willing to sell a CE ticket on the plane, given the moveable curtain)? And are they good (for the same number of Avios) from deep discount coach fares, including HBO?
UuA are available from all but the lowest fare buckets, regardless of HBO. So about half of HBO tickets sold would be UuA eligible. Anything other that O, Q, G fare buckets - so UuA includes N, which is often fairly cheap. So on LGW-EDI, £41 is O class, not UuA eligible; £47 is N class and is UuA eligible. Both are Basic (HBO) fares, the cheapest N fare LGW-EDI which is Plus is around £54. More details in the Using Avios sticky on the front page.
They do require redemption inventory but within Europe, and avoiding peak holidays / commuter flights, CE redemptions are pretty widely available, even on the day of travel. It's not quite the US system of any available seat, there are some revenue management nuances all over this, not least because sometimes CE redemptions are available on overbooked flights, so some BA crew who live out of London use Avios to avoid impossible staff standby queues.