Wagons for locomotive yards?

[Bryan]

Had another think on this one.
I believe Alnmouth had an allocation of old Conflat wagons to use as barrier wagons when propelling Loco Coal wagons up on to the coaling stage as locos were not allowed on the stage.

With regard to lettering.
All taken at Newbridge NYMR

On the LNER BV lettering we still have the un answered question as to what should be inside the White outlined square box. between the number and the ducket.
We have seen photos with XP in some and other shots with other letters.
What is correct for this Brake as outshopped from Shildon in 1964 after repair / overhaul?
As this is the period we are basing it on.