It's a Derby-built Class 108 dmu. Surprising the shots of Norfolk with a destination blind for what appears to be a Norwich-based set, because as far as I recall the 108s were never in use there. By it's cleanliness the car appears brand new. Two of the oncoming trains are Britannia-hauled, with mixed BR/LNER stock, so presumably somewhere on the GE main line.
Notable how just about everybody, men and women, is wearing their formal suits (even the ganger in charge of the track crew), and apart from a few selected children are all middle-aged or more.
The big windows were indeed a selling feature. I have to say in many decades of riding these trains I never saw anyone messing about distracting the driver, such events must have been few and far between. For a long time hardly any of them pulled down the blinds, even at night. Then there was an accident, on the Chiltern Line, and an enthusiast seated there gave evidence which contradicted the driver's initial version, and which the inspector had reasons to believe. After that I don't think I ever experienced another Chiltern set without the blinds pulled firmly down, and it unfortunately spread elsewhere.
If you got a winter Sunday afternoon run on a quiet branch, with just you and parents seated behind, the driver might well slide the door back, have a kindly chat, and then let you have a go, initially sounding the two-tone horn, then graduating to the controls. My own experiences were, inevitably, down the Minehead branch. I wonder how many current drivers had their first ever experience that way.