There should be a fully investigation into this. The UK secret Police are unaccountable. Even in the 90s it was going on. So if Paddy got a bit uppity and wanted his rights on the building site or was an active trade unionist etc, he found himself on a blacklist.
MI5 linked to blacklist of Irish workers - The Irish Times - Wed, Oct 24, 2012
IRISH CONSTRUCTION workers were blacklisted by British construction companies during the 1970s with the help of British intelligence services’ records, the UK’s information commissioner suspects.
Such files, he said, were more commonly held by the Consulting Association on Irish workers, who were being monitored more closely by agencies such as MI5 during the 1970s at the height of the Troubles.