Class 27 (Birmingham Railway Carriage & Wagon Company 1,250hp Type 2 Diesel-Electric)

The Class 27 was a development and follow-on class of Type 2 diesel-electrics from the pilot-scheme Class 26 (which ironically outlasted the 27s). Compared to the earlier locos the Class 27s had a slightly uprated engine, different electrical equipment and an increased top speed [1]. The most notable visual difference was that the Class 27 had a headcode box above the cab. Originally the Class 27s were allocated to both Southern England and Scotland but later on the locomotives were concentrated in Scotland.
D5410 at Kidderminster Town

Information
Number built: 69
Built: 1961-62
Builder: Birmingham Railway Carriage & Wagon Company
Engine: Sulzer 6LDA28B diesel
Power: 1, 250 hp (932 kW)
Wheel arrangement: Bo-Bo

The original locomotives were the 27/0, two sub-classes were later modified for express services in Scotland. Some locomotives were modified for push-pull operations as the 27/1 and some with electric train heat as the 27/2. One of each top and tailed Edinburgh-Glasgow expresses in the 1970s [2] however their reliability suffered on these duties, a number of 27/2s catching fire. 

By the end of the decade they had been replaced by Class 47/7s [3]. The Class 27s were gradually withdrawn throughout the 1980s with the final withdrawals in 1987 however eight have been preserved.
Another view of D5410

27 001 at Tunbridge Wells West

[1] Brian Haresnape, Production Diesel-Electrics Types 1-3 (Ian Allan, 1983) p. 40
[2] Chris Heaps, BR Diary 1968-1977 (Ian Allan, 1988) p. 45
[3] John Glover, BR Diary 1978-1985 (Ian Allan, 1985) p. 27