https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/695321/An_inspection_of_exit_checks.pdf
https://publications.parliament.uk/pa/ld201719/ldselect/ldeucom/9/9.pdf
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/704057/Policy_Note_-_Exceptions_and_Licences.pdf