http://researchbriefings.files.parliament.uk/documents/CBP-7484/CBP-7484.pdf
http://www.oecd.org/fr/emploi/emp/Editorial-and-executive-summary-FR.pdf
http://foodresearch.org.uk/wp-content/uploads/2016/07/Agricultural-labour-briefing-FINAL-4-July-2016.pdf
https://www.boe.es/boe/dias/2021/12/30/pdfs/BOE-A-2021-21788.pdf