This is a microsite run by TMP. Since most Applicant Tracking Systems (the software used to list/fill jobs) do not list jobs in an SEO friendly way, companies like Jobs2Web, Optijob, and TMP built microsite products like the one being used here by the GCHQ.

TMP is an ad agency, not a technology company - can't say I'm too surprised they missed the ball on this one. There are lots of US gov't agencies who use TMP also.