I don’t find it particularly surprising that the difference in earnings between those with degrees and those without is much lower than it used to be. After all, many more people are attending university in the U.K. than ever, and the types of course that the majority decide to take (arts & humanities) are less likely to end up with them in high paying jobs.
However, where there is a shortage in skills, in disciplines such as mathematics and science, it’s likely that earnings will remain relatively high compared with other graduates. Like many things, it all depends on the laws of supply and demand.