http://researchbriefings.files.parliament.uk/documents/CBP-7484/CBP-7484.pdf
https://www.boe.es/boe/dias/2021/12/30/pdfs/BOE-A-2021-21788.pdf
https://www.etui.org/content/download/36217/363575/file/F-B_07_EN_WEB.pdf
https://www.tuc.org.uk/sites/default/files/Brexit%20Legal%20Opinion.pdf