In message , at 20:39:00 on Tue, 31 Dec
2019, Bryan Morris remarked:

Now that we know it's one of the weekend-only tickets, it's
entirely possible the gates won't accept them. But then you'd think
the staff would be used to letting people through manually.

Maybe he was just fed up with the number of people requiring exit
assistance.

The OP was requiring entry assistance.

Nope it was my return to St Pancras I needed assistance in getting out

Thanks for the clarification (I'd jumped to the conclusion that "when I
came back" meant getting on the train at Bedford) which means you were
proffering a London Thameslink ticket at a London Terminals barrier, but
as discussed it's effectively just as valid.
--
Roland Perry