Earlier quoted context omitted.
The bump in CS uptake was due to the dotcom boom rather than any long term trend. CS still has a higher average salary than most other subjects.
"CS still has a higher average salary than most other subjects." Right, but don't qualified UK developers now have the option of working anywhere in the european community without complicated work visa hassles. Perhaps for a job that requires specialized skills the competent ones are going to where the jobs with reasonable salaries are. Which is not the UK.
There are tiny spots where you could earn an American-level salary as a software developer, but generally speaking it is a European rather than a UK phenomenon.