Common Misunderstanding
People often fail to understand why government IT is always horrible, but I'm betting the issues plaguing the UK are the same as we experience here in the US. Namely, pay. The president of the United States only gets paid 400k to be the CEO of 330 million people, most CEOs wouldn't bat an eye turning that down.
Government positions don't generally pay well - they are stable, but usually the work is simple and mundane. Not the kind of stuff it takes a genius to do. The public also does not want to see public employees running of to the bank with gobs of cash, so what does an organization do when it has a requirement for a special type of worker that it can't properly compensate within its pay range without overturning the apple cart? Contractors.
If you look at the government pay scale, managers don't want their employees making more than them because it looks fishy, but in reality the employees might be doing more demanding, more difficult work which the private sector would pay them much more for.
So now the only people accepting government IT positions are usually those who are really just politically ambitious or aren't skilled enough to compete in the private sector, and since they are actual government employees - they are the ones actually in charge and making decisions for their more capable contractors.
They also know they aren't as capable, and are terrified of making a decision which could blow up in their faces, so they spend all their time trying not to make any - and just stay the course.
If the UK wants quality work, they can either augment their salary tables to make government positions attractive to capable people or just subcontract all that work to large defense companies like the U.S. generally does.
Source:. U.S. defence contractor that makes more than the vice president of the United States and is also sick and tired of dealing with inept government IT workers.