Part Pay with Avios.
British Airways do something called Part Pay with Avios. It is a scheme where you can, should you wish, offset some of the cost of your flight with Avios, the virtual currency. If you are not sure what Avios are please read my How to Collect Avios page, where it is explained in greater detail.
So, how much can you save? Well, it depends on which class you are travelling for instance and on which routes. I will use a Business Class Europe measure. In this instance, called Club Europe to BA.
To explain, as you can see in the screenshot from British Airways website, you can get anything up to £200 off a flight. I find the part pay, more often than not, a better use of my Avios than paying for the whole flight with them. You may have Avios coming out of your ears for instance, so it might make more sense to use them that way!
The sharp-eyed amongst you may notice something on the above table. It must be remembered, the more you spend, the less value you get from your Avios. For example, to get £100 off you have to spend 15,000 Avios. You’d expect to spend 30,000 to get £200 off? Nah, it actually costs you 36,500 Avios. That is, to clarify, just the way it works.
Using Part Pay with Avios
I shall use an actual booking I made, by way of an example to demonstrate how you can reduce the cost of your flight.
For example, above, from London Gatwick to Bordeaux in club cost £222.60. Then this offer below hoves into view as you complete the booking process. It will, of course, ask you to log in if you are not already logged in. This is so it can tell you your current balance and what you could use to save money.

Part Pay With Avios
To demonstrate, I have chosen to use 15,000 Avios to get £100 off.
The advantage of using part pay with Avios, as opposed to paying for it all with Avios is that you will still earn Avios and Tier points on your flight. Yet this is something you won’t get if you choose to get a reward flight if pay for all of it with Avios.
Part Pay with Avios when used specifically in conjunction with British Airways Low Fare finder tool can make some fantastic savings for you. If you are not restricted by date, find the cheapest flights that month and then use some Avios to get them even cheaper still!
British Airways Page on Part Pay with Avios