Recruiters sometimes advertise nonexistent jobs, or existent jobs at nonexistent rates, to get their foot in the door. I wouldn't necessarily take advertised jobs/rates on jobserve at face value.
I have noticed this. There seems to be a massive gap between the finance sector and everyone else. I'm not too sure what to make of that. For the sake of comparison, the average salary for a Software Engineer at Google in London, according to Glassdoor (before bonuses) is £45k.