Thank you. I have already seen that and it is from 1962 onwards that I am looking for, when the Vulcan Foundry numbers would have been prefixed by a D or an E, which actually started before 1962 but carried on well past that date. It does seem that the lowest D number was D46, which corresponds to Drewry 2217 (LNER DS1173), and digging through the records shows all diesels before that to have regular VF series numbers.