So, let me summarize
For "economic and technical reasons," the service could not be provided by any organisation other than the original contractor before the expiry of the Horizon Agreement
Okay, sure, that part I can accept. It would be highly unreasonable to throw everything away and have operation grind to a halt while you commission Crapita (because who else ?) to develop an entirely new set of bugs.
So fine, ensure the maintenance of your buggy, mololithic, outdated system. Got it.
Meanwhile, now that you have ensured its continuance, WHAT ARE YOU DOING TO REPLACE IT ? Now's the time. Throw another £100 million to somebody and get your non-monolithic, up-to-date, designed for multi-channel digital operations (do you really even know what that means ?), highly Agile system on its feet so that you can replace the dinosaur when the next end date expires.
Because 2024 is going to be here before you finish drawing up your next set of outdated specifications, I'll wager.