Bletchleyite
Veteran Member
No ticket check will ever be 100% secure. A balance has to be struck between revenue loss, staff time taken to undertake the check and passenger inconvenience. As a passenger I wouldn’t take kindly to a ticket check at the Euston barrier only for another check before Rugby just in case someone had boarded at Cheddington and changed into an Avanti train at Milton Keynes, especially if this was to happen frequently.
What you tend to find with Avanti is that most staff won't bother checking if you've boarded at a gated station (e.g. Euston, MKC) because that's a double check anyway, other than a tiny amount of leakiness as you mention or the odd person on the wrong train (which at MKC is fairly unlikely because it's one an hour to each of three destinations). In those cases 1st and SP will be checked as a priority as a gateline won't check that.