They were both of 0-6-0 wheel arrangement and were fitted with English Electric 6RKT engines of 500hp. They were painted black with an orange stripe along the middle of the bodyside, which turned into a 'V' at the nose end. The major difference between the two locomotives was that D0226 had diesel-electric transmission and D0227 had diesel-hydraulic transmission.
BR tested both locomotives at its Stratford depot in East London. D0226 has been preserved at the Keighley and Worth Valley Railway, but D0227 was scrapped.