I have a Rail Electric Unit Stock book, May 1990
It had:-
304 Allocated Longsite (Sector PLGX Regional, longsight, livery Blue/Grey) 23 units
303 same as ^^ 4 units
310 Allocated Bletchley (Sector Provincial, Bletchley, livery, provincial) 10 units
319's had come to Thameslink (Allocated...