The root cause of this issue though is that the railway has not expanded the train describer systems used for the
train reporting numbers from the 1960s system. Which is a four digit system, where the original specification was:
First digit, a number between 0 and 9 - the train class, noting that the classes have been revised over time.
Second digit, a letter (originally a subset of the alphabet, only ten different letters on some systems).
Third and fourth digits, both numbers between 0 and 9, combined, the individual train identifier / number.
Modern, computer based train describer systems can now support any normal alphabet letter or number in any/all four digits. As can be seen when signallers use the system for reminder words/codes rather than train numbers.
Where the train describer systems use computer monitors, there is no real reason now to restrict them to four digits. I have been of the opinion that any new train descrber systems should be specified to have six digits. Thus, once these are widespread, six digit train reporting numbers/code can be introduced.