I think some of the GW branch shots are on the Cambrian, the Blue Pullman and Mainline GW shots are on the London Paddington to Snow Hill services...
Not all the footage was contempory... have a look at the loco at 6'17"... its the LMS Turbomotive 6202.. note lack of cylinders!! Also the shot of Jubilee 'Barbados' is also in LMS livery....
As for other locations I reckon Lune Valley and the section where the West high famously runs parallel with a main road (I forget where) ::)
look at 6'51" - 2" excellent ... def 6202 Later rebuilt as 46202 Princess Ann - wrecked in 1952 at Harrow and Wealdstone disaster soon after rebuilding!
Aaaaaaaaaaaaaaaaaaagh Creeper!!!!!