Why did United Kingdom licenses require cloned human embryos to be destroyed by the 14th day of development?

In the United Kingdom, licenses for research involving cloned human embryos mandate their destruction by the 14th day of development because this timeframe marks the emergence of the primitive streak. The primitive streak is recognized as the initial indicator of an organism's nervous system development.1

This regulatory limit is rooted in the ethical principle of providing special moral consideration to the embryo during therapeutic and research cloning. By restricting research to this early stage, the Human Fertilisation and Embryology Authority seeks to balance the moral imperative to advance scientific knowledge regarding human development and disease with the ethical necessity of preventing the development of an entity with the potential for sentience.1