Hi, DaveF, another excellent set of photo's. Good to see the Newton Chambers car carriers, saw them myself at York when there in the late '60's. Also that class 120 DMU seems to have a plain blue trailer buffet car, which I think is quite rare.
Regarding the ex-LMS BG, the reason for the plain blue livery is that being non-passenger coaching stock, such vehicles were not given the 'inter-city' blue & grey. I think this is covered in the Mark1 carriage book, when liveries are being discussed.
Please do keep the photo's coming.
All the best,
Market65.