Yes probably that was the reason for a Class 31 invasion. Though in 1974:I think the 31s took over from Hymeks ?. I remember circa 1975 seeing the last of the class lined up at Old Oak Common. Cleared the class as they appeared in my Ian Allen book in one go (ignoring the 85% or so already long withdrawn)
22/8/74 31264(IM) 4B07 1507 PADD to BTM parcels.
37049(SF) 1233TTho STJ to Dagenham empty cartics
1065 1A19 1100 Penzance to Paddington Cornish Riviera and it's soon to be replacement 50019(BR) 1B83 1530 Paddington to Penzance.
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