<ul><li><a href=http://www.legislation.gov.uk/ukpga/2003/21/contents target=_blank>Communications Act(Communications Act 2003, last updated in July 2003, s. 87)</a></li><li><a href=https://www.ofcom.org.uk/__data/assets/pdf_file/0020/108353/final-statement-narrowband-market-review.pdf target=_blank>Wholesale Voice Markets Review 2021-26(Sect 6.89)</a></li></ul>