"false self-employment"
Beware the mythical status of "self employment" that is peddled by some of the less scrupulous agencies when they place you with a single employer.
Under UK tax law you cannot claim "self employed" status if you work solely or predominantly for one employer. Just ask the tax office. Its very easy!
You may well be able to do so under other tax systems (Irish perhaps?) this is probably how such agencies get away with these extravagant claims. They'll have a weasel paragraph in the small-print though. It is up to YOU to check the tax situation, not them. After all, as
you are
self employed they don't employ you - so how could
they be responsible for
your tax affairs?
And as bfisk says, beware lest you are caught - it will be VERY expensive.
And dream on if you think having a professional qualification exempts you from tax on further training. As if! What planet do these ideas come from?
Caveat Emptor, P2F fool.