(31 May 2015, 10:59 am)mb134 wrote What was the aim of it, and why did the North East put them back into 4 digits?
I don't actually know - the ironic truth is, 1307 never actually reached Scotland (it was stored at Blyth for months after refurbishment) and is actually on its fourth fleet number, having started as 1518 it became 44007 when it entered service at Ashington before becoming 1507 and then 1307. Of course, apart from 44007, 3 of its numbers are pre-used numbers.