@jgw1 Why do employers not want permanent staff?
One aspect is the same reason that supply teachers, locum doctors, and agency nurses exist. It's to cover staff absences, peak demand, and particular short term projects. Not to mention where the "permanent" jobs simply aren't popular and never get many applications, or where there are seasonalities.
We've come a long way from the old days when everyone worked fixed regular hours in "jobs for life". Nowadays, huge swathes of the employment market are flexible.
Unfortunately, the tax rules aren't keeping up with the modern working life, hence stupid damaging rules like IR35 which arose in 2000 because of stupid damaging employment rules in the 90s, and so it goes on.
Of course, not helped by Gordon Brown encouraging people to set up limited companies with all the tax breaks he created in the early noughties which only applied to limited companies, so caused huge numbers of sole trader window cleaners, electricians, dog walkers, etc to convert to limited companies!