If you follow the instructions, which aren’t bad, on getting the NHS app (not the NHS Covid app!), and obtaining an NHS login (if you haven’t got one already - you’ll need your NHS number to register), and then navigating through the App to the covid vax status of yourself. you can also Add them to your iPhone wallet (not sure about Android), at that part of the App, which makes it a bit easier to show when asked - don’t need to relogin to NHS app.
Big note:
You’ll need to do this monthly however (app into wallet), because the vax status QR code only lasts 1 month.
As someone said you could take a screenshot of your covid QR pass, but that is the same, and expires in a month. If you always login to the app, the QR code in the app (only), will be automatically updated to a month ahead. But be aware you’ll need a data signal to access the internet in the App… so probably better to get it into iPhone wallet/take pic beforehand.
so, it’s just another thing to add to the list of stuff to check before heading off to the match:
Keys
Money/cards
Phone (charged)
Teeth/glasses
Tickets ok
Vax QR codes up to date.