corporate-wage-slave

There are 3 UK airports that use biometrics on domestic travellers, LHR (at T5 and T2), LGW (North and South but different systems) and MAN, and I've seen problems very occasionally at all 3 locations. It's fairly rare, the usual problem at LHR is a changed booking (e.g. SDC airside), but yes there are occasionally technical outages too. The worst one I can recall was where a NCL service had half boarded - and I was in the first half, unusually - and the system stopped totally. There have also been outages at the recording stage so that no domestic passengers can enter LHR until it was resolved. And then there was a case of a woman and child with a Geordie accent so pronounced that I could identify which of a dozen streets in Wallsend where she came from - and yet a UK Border Force person was sent over to verify she wasn't an illegal immigrant. We all waited 30 minutes for this to be completed. There used to be a problem - now fixed apparently - where if people went through the system too quickly when the server was running slow that the pictures would go out of sync, one person getting no biometrics attached and the next traveller getting the previous person's details.

In your case, it's probably only going to happen to you once in your life (on the basis it hasn't directly happened to me yet) and it was just a slightly annoying delay. It's even rarer for people to be offloaded on to another flight since usually there is checked luggage involved, which would have to be offloaded too.