Authorities found one illegal worker at one of Chez Gerard's London restaurants while two workers were found in Pizza Hut outlets in Reading and Hounslow.
A spokesperson for Pizza Hut told the Telegraph: "This particular incident took place almost a year ago at one of our franchised stores. We have since ensured that all our franchisees have reviewed their processes, in order to prevent this happening again."
Some 1,161 firms, mainly restaurants or takeaways, have been fined nearly £10m for flouting employment laws by hiring 2,058 illegal workers, figures released by the UK Border Agency revealed.
Tory MP Ann Widdecombe, the former Home Office minister, said overall figures were the "tip of the iceberg" and criticised the government for ignoring the magnitude of illegal working.
A UK Border Agency spokesperson added that employment of illegal workers "is a crime that not only undercuts local businesses but also has a serious impact on local communities, taking jobs from those who are genuinely allowed to work".
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