Depending on your ticket type, you might be able to upgrade to a nicer cabin by calling up BA and asking. They will give you an option of upgrading for cash or with Avios. This will usually be quite expensive, but occasionally there’s a deal to be had.
However, when the flight starts filling up, there’s a chance BA might over sell the cabin you are in. When this happens, they will start being forced to upgrade people, which begins with making a good offer for a low-cost upgrade. I.E. they will try and make some money out of it before they give out free upgrades.
Keep an eye on your booking by checking the BA app or logging in to the website regularly. A common occurrence for short haul is for economy to be oversold so people need to move up to business class. A normal price would be £90 to £180, which could be a good price if you don’t have silver status or above, as it will give you lounge access and priority treatment, not to mention the better tier points. For long-haul the offers can range from over £500 to as low as £250. But of course, the seat difference if you’re upgrading into Club is huge!
Deciding if you go for these offers can be a bit of a lottery, because if you don’t there’s a chance you might get a free upgrade or you might be stuck where you are!
Free upgrades!
This generally doesn’t happen until check-in, but if, for example, economy is oversold, premium is full and business has empty seats, then they’ll start moving people forwards. It could be at check-in, after check-in or even at the gate. The magic ding at the gate when your boarding pass gets rejected, they rip it up and a brand new one appears with your shiny new seat in business class is a great feeling.

Who gets the free upgrades?
Well BA have a scoring system that gives every passenger a rating. They then simply start at the top of the rating list and work down.
How they score you is a bit of a mystery, but some things that are certain, your Executive Club status instantly puts you in a good position on the list. Put it this way, gold members probably are getting upgraded first. But there’s more to it than that, how much you spend in general does seem to be a factor. There are other things that count, if it’s your birthday you’re likely to be upgraded, also if you’ve just earned a new status, like just moved up to Silver, again that increases your chances. They like to tease you with flying in better cabins. There’s also a theory that silver might get more upgrades than gold because they are less likely to buy business tickets and it’s a way to incentivise them. Whatever the reason, you can get upgraded without warning, and it’s great when you do.
Can I be downgraded?
Yes, very upsettingly, it is possible to be downgraded, even if you’ve paid for a full price ticket in a higher cabin. When they oversell flights, they will move people around where they can. In the airlines mind getting you to do your destination is the most important thing. So, if they can sell 24 tickets in business class and there’s only 22 seats, then they’ll downgrade the person who paid the least or has the lowest status. When this happens, you do of course get a refund for the difference and most times you will be offered a different flight in the cabin you originally booked in. I would always also complain, as they will usually award you some Avios points as well as an apology.
Bottom line
Upgrading without offers can be expensive. Watch for the special offers, take them if they are a good deal or if you particularly need them (like you need the points or it’s a night flight and you want a bed). Or risk it and wait, you never know when your seat might change at check-in, or you get the magic ding at the gate!