The UK's Human Fertilisation and Embryology (HFE) Act 1990 (as amended), in the Code of Practice established by the HFEA (hereinafter the Authority), defines third party agreements as follows:
For the purposes of this Act, a “third party agreement” is an agreement in writing between a person who holds a license and another person which is made in accordance with any licence conditions imposed by the Authority [...]
Third-party agreements are required in all cases before starting a fertility treatment using donor gametes or embryos.