Rules that came into force yesterday requiring employers to make more rigorous checks on foreign workers are unfair on small companies, which will be expected "to act as immigration officers" and face "huge fines if they slip up", business leaders have warned.

The government is adopting a tougher attitude towards employers, including imprisoning executives who knowingly employ an illegal immigrant. The penalties are part of a new immigration points system. The first phase of the system - affecting highly skilled migrants- is being introduced.