Illegal immigrant duty to inform authorities

[ukbane]

Hello
Is there any legal duty to inform the police or home office if you suspect someone of being an illegal immigrant.
Someone I know is making an application to stay here on compassionate grounds. His solicitor has asked him to secure some references confirming how long he has been here etc. I am happy to do this but I am slightly concerned if there is a duty to inform the HO if you suspect someone of living here illegally. Is this the case? Could I be liable for something.

[vinny]

Answer.

[secret.simon]

How do you know the illegal immigrant?

There is a legal duty on certain specific people (employers, landlords, banks; etc) to not provide services to illegal migrants, but there is no legal duty to report them to the authorities.