Can I use Virgin Trains between Watford Junction and London Euston?

[Starmill]

Though why it is issued like that utterly confounds me, and it is a massive anomaly as the fare from WFJ is much higher.

Well exactly. This is precisely the point.

It also manifests itself in the case of Brentwood, but there it's handled by an easement that forbids boj at Shenfield. That solution seems to work perfectly well.