It is not targeted only against this individual. It is broadly applied to anyone trying to enter and settle in the UK: all sorts of soldiers, doctors, nurses, firefighters, and others who have served (and may continue to serve) the UK armed forces and public services. Also computer programmer, engineers, plumbers - all sorts of people that contribute to the UK.
The very high fees for entry visas or settlement, further raised by the "NHS Surcharge" (when all these people pay the same taxes for the NHS as a native born Briton, sometimes more), are simply there to keep out any foreigners who are not rich. It doesn't matter how useful you were to H M Government or how useful you are to UK Plc, all that matters is that your wallet is bulging. Got several thousand pounds to spare and all your paperwork exactly in order? You can stay! Been a hundred times more useful to the UK than most of the people who sit on the front benches of the House of Commons but your wallet's a little lean now? Bugger off!
This chap we're talking about couldn't get citizenship because he didn't have thousands of pounds to spare.
It's a Hostile Environment - Hostile to All. Except the rich.