Look at the salary on offer. This is for a dev/data job in Cambridge. The market rate for a senior developer here was around that level in the early 2000s. Today that would be a big pay cut for almost anyone with even the "essential" skills and experience.

The British government and public sector are constantly limiting themselves by being unwilling to pay market rates for the skills they need. Then they contract out needs like tech to work around the bureaucracy - but they demand so many strings attached that the little guys who are more cost effective don't want anything to do with it. And so they mostly outsource to large firms or sometimes specialist agencies who have jumped through the hoops to get all the right certifications. Naturally those suppliers are in a position to charge premium rates even for relatively simple work.

If the Civil Service built up a capable IT function staffed by properly qualified and experienced people that would surely save billions in budget and years in timescales for some of the (in)famous government IT projects and probably significantly increase the odds of successfully delivering something usable at the end of them. But as anyone who's working in our Civil Service can tell you the emphasis on ranks and pay scales and other very specific rules about career advancement are unlikely to go anywhere any time soon. Even if they did the culture of people moving around the Civil Service like interchangeable parts instead of building up deep expertise in specific areas would still be a problem.