Wages for the lower / middle paid are suffering from a double whammy.
The huge expansion of university education in the late 90s (to manipulate the unemployment figures) created a lot more people holding degrees. But, the government of the time did nothing to invest or incentivise investment in sectors like technology that would then absorb all these graduates. Instead the increased supply just put downward pressure on the graduates jobs that did exist, and displaced graduates into what had traditional been non graduate jobs, depressing those incomes as well. But, those at the bottom have been lifted (rightly) by increasing the minimum wage and the personal allowance. Result, little extra return for being a graduate. And of course, the other impact of more supply was downward pressure on pay rises for promotions as well, as there were more people chasing each one.
The second big disrupter of salary growth was the enormous transfer of wealth from the public to the private sector under the Blair / Brown government from tax credits. These have now morphed beyond all expectation to put further downward pressure on wages / salaries and distorting the jobs market massively. Some roles apear shockingly paid, and as a single person, or a couple without children, they are. But after you roll in the government subsidy they become much better, or even very well, paid and companies can fill the jobs without spending the market rate. But, a large number of people can’t access the subsidy, and therefore the job.
The impact of both depresses salaries and career progression in much of the public and private sector. Subsequently government have tried, with varying enthusiasm, to address the investment in growth (though, not this one…) to address the first. No one has the appetite to unpick the second.