Last but one time we came through airport security, the guard put big red marks on our boarding cards which I was storing inside each passport foreasy access...the red pen stained the photo page of each passport slightly, but everything is still readable underneath.
WWYD? We have used them once since - Easyjet - and are due to fly Virgin in 3 weeks. Have checked UKPS website and it says some airlines may be fussy even if they are still totally readable (which they are)
Am panicking as seems a bit late to change them but am worried we may not be able to fly...