Lots of people have, BA do it every single day - indeed you can find a thread dedicated to it here: https://www.flyertalk.com/forum/brit...rade-week.html

Now, that was the good news. Here comes the not so good......

BA won't upgrade you because you ask nicely, or it's a special occasion, or you are wearing your best suit, or you've handed over a envelope with your boarding passes in it and a cheesy "Please upgrade" stamp on it, or any other hoary old tricks that you might read about.

BA will upgrade you because(*) it needs your seat - and it would need your seat because it has sold more tickets in that cabin then there are physical seats so some people have to be moved. So they will move some people into the next cabin up to make the numbers work (and next cabin down on the much rarer case where going forward won't work). This can obviously have a knock-on effect, where some people get upgraded into WTP but now there aren't quite enough seats in that, so some lucky WTP passengers get into CW etc.

And all that is decided by computer (you may see references to DUT - Discretionary Upgrade Tool), not by check in agents. The algorithm it uses is deliberately opaque so people cannot 'game' the system. The only thing you can really do is fly in cabins that are frequently oversold. WTP seems to be the "sweet spot" for this, it's an increasingly popular cabin amongst passengers it seems, and on many planes it is quite small so they end up having to move people forward. But more bad news - on the refurbished 777s it has been increased greatly in size to accommodate more people....

In essence, don't get your hopes up. As the oft repeated mantra round here goes, "pay for the cabin you're prepared to travel in". If you want to purchase a paid upgrade, there are some options available that might end up being cheaper than buying the ticket in the cabin originally (but can also be more expensive). People will happily give advice on those if it's something you are considering.


*They sometimes seem to upgrade as service recovery even if the cabin is not full, I've had that once.