Amendment NC16 says

Earnings of workers supplied by service companies ...

(1) Regulations may make provision for securing that where -

(a) an individual ("the worker") in any specified circumstances personally performs, or is under an obligation personally to perform, services for the purposes of a business carried on by another person ("the client"), and

(b) the performance of those services by the worker is (within the meaning of the regulations) referable to a contract between the client and a third party,

relevant payments or benefits are, to the specified extent, to be treated for the purposes of the applicable provisions of this Act as earnings paid to the worker in respect of an employed earner's employment of his (where they would not be such earnings apart from the regulations).

Or, in english -

If an individual performs services for a client then that individual is considered to be employed by the client and the client will be assessed for PAYE and NI on all payments to the individual.

The amendment then goes on in several sub clauses to say -

Stuff the legal position, we will re-write contracts for tax and national insurance purposes and if that does not work, the Government will change it to make it work.