Agency want to change T&C saying I do not have a PSC

[malvolio]

The legislation does apply to us as it boils down to if a company pays for labour via any means other than paye it has to be separately reported to HMRC stating both the name and NI number of the person providing the labour and the details of the company to which the money was paid to.

From memory and I'm on holiday so not hunting through paperwork (while the others are spending money in a quilting shop) it also impacts us if we subcontract work and don't pay via paye

Not quite. Much of the required information is only required if you are paying a Sch D self-employed, partnership or LLP-based worker, not a limited Company. More detail here

But nobody expects an agency to do anything than apply all rules to everyone regardless, do they.