And what will replace the T1s which are still needed for service?
The H4s that were converted to work service were only done in the last decade or so, post-retirement in January 2012. There was one that I even photographed undergoing conversion as late as 2019- note the original number plate, meaning that the car had not yet seen any use as a work car.
View attachment 684949
If they received an appropriate level of TLC prior to being cleared for work service, it would be far too soon to discuss their replacement.