Its worth seeing what the Derby Sulzers site has to say about the decision to purchase the 33
https://www.derbysulzers.com/class33.html
"
In placing the specifications for the Type 3, the Southern Region had a very clear idea of what was required, including some features which were outside of the BTC's specifications. These requirements included:
Haulage of 700 ton freight trains on ruling gradients of 1 in 70
Haulage of 375 ton passenger & van trains over electrified and non-electrified routes
Fitting of equipment to provide electric train heating
Ability to haul electric multiple unit stock at normal speeds over all routes in times of emergency
Maximum service speed of 85mph
Ability to work vacuum & air-braked rolling stock
A wide route availability
The BTC Class 3 specification included two contenders, the 1,750bhp 105 ton Co-Co 12 cylinder equipped offering from English Electric or the 1,550bhp 76 ton Bo-Bo 8 cylinder equipped offering from BRCW. The BTC were in favour of the English Electric design, wishing to make it a standard design, but the Southern Region favoured the BRCW design from the outset on the grounds of weight & cost. It also offered the requested dual braking equipment, the electric train heating function and had a better route availability. The BTC held out for a maximum speed of 80mph but agreed to the fitting of dual braking equipment, an awkward about face following their recent decision to generally retain the vacuum brake as standard."
Its also interesting to see how widespread the use of the 26/27 fleet was outside of Scotland
https://www.derbysulzers.com/class26.html