I don’t mean to belittle you but failing the lung function test has nothing to do with your firefighter and physical fitness background. You could have gone through the whole National Service ordeal with a lesser than average lung function but did not realise it was so.

But, maybe your technique was wrong. The sad thing about the lung function test is that they do not get you to do it multiple times. Which means that if you messed up and understood the instructions wrongly, you can’t have another go. Maybe you should contact the clinic to ask if you could take it once more.

It’s best to see a specialist just to be on the safe side. You could see this as a good opportunity to learn whether or not you actually have a below average lung function.