Apologies for resuscitating an old thread, but I do think you're right that blue and grey lasted into 1997 on Merseyrail. I was but a kid at the time but I do seem to remember riding a blue and grey 508 that year and thinking what a survivor it was.
I'd be really interested to know what was the last serviceable Merseyrail unit in blue and grey. It has to have been the last non-heritage example of blue and grey running anywhere in the country, surely?
I've never been able to confirm it for certain with 508112 and 508139 both suggested by different sources. A bit of researching old photos has shown that as of April 1996, the following were still in blue and grey: 507004, 508112, 508125, 508130, 508134, 508136, 508137, 508139 and 508141.
The latest date I've found is 28th September 1996 with 507004, photo copyright Ryan Tranmer:
https://www.flickr.com/photos/60628514@N02/49822151758/. Can anyone advance on that?
Additionally, 507/8s were still being repainted into blue and grey into summer 1991. Hadn't the rest of the network long since abandoned repaints into this livery?