Presumably Prospect agreed to this as well ? If so, why ? It's the thin end of a wedge.
I would suggest it's a pragmatic use of resource. There are no UVC's running whilst the unit gear up for EFD OCT2, so no 'work' for TATCs. There is a shortage of ACPO and FSS for OCT2 so why not make use of the available resource and pay them a decent wage. Once OCT2 is finished the UVCs start again and the TATCs can then do what they were employed to do.
It's a short term solution for a short term problem.
BD