The use of an agency in this manner not only relieves the Company of the admin burden of the payroll but also provides a means to ensure that the taxes due are collected and thus avoid the types of problems Ryanair guys had with setting up bogus shell companies to avoid tax. As we know the Ryanair system was slammed by the courts as tax evasion and at least NAS are avoiding such possible events. If NAS wanted to be the employer probably they would need a UK based company NAS UK ltd for instance just as Cathy have CX UK ltd.