What couplers do the mark 3s have (both loco+DVT and IC125 variants if different) within rakes compared to the mark 4s? And would fitting loco-compatible couplers to mark 4s be a big job?
If that's the case then isn't it even more daft for other ROSCOs to store mark 3s? I thought a huge number (of mark 3s) have been off-leased from FirstGWR but I've not heard of (m)any going for scrap. Mark 4s, being PRM compliant, have to have far more potential for future use than mark 3s particularly given that both designs of power door retrofittment for mark 3s have proved problematic. It makes sense to me to have some stock stored in reserve for future requirements and mark 4s would surely be a better choice than mark 3s.
Different ROSCOs.
Angel have been successful in finding new uses for a reasonable number of their ex HST mk3s in the short sets. Angel/Wabtec have the current door retro fit IP.
Porterbrook have stored their ex HST mk3s. No realistic future.
Eversholt have all the mk4s. the original expectation was that 6 sets (+ spares?) would be retained by LNER then TfW and the Blackpool Open Access operator are using about another 4-5 sets worth, however LNER recently said they would be tendering for new stock. So only 15% of the fleet with a new home.
Storage is in short supply at the moment with all the new stock piling up and lots of old stock stored hence the price will have gone up in places in order to get new storage on line.
Eversholt /LNER will also know which coaches are in a worse state that the rest and hence worth canabalising. Scrapping a few may actually generate enough spares to keep the rest going reliably (i.e. so parts can go away for overhauls on rolling basis). At 30 years they will know which are the worst.
Some of the coaches involved were renumbered post Hatfield but those 2 don't appear to be those.