United Kingdom Border Agency - Home Office

The United Kingdom Border Agency (UKBA) is responsible for enforcing immigration and customs laws throughout the remnants of the British Empire. Their website (linked to above) has instructions for reporting illegal immigrants and the smuggling of goods that can be summed up as sending email to two places although you can call 800 59 5000 to report smuggling.

UK Border Agency Contact Emails

Report Illegals: UKBApublicenquiries@ukba.gsi.gov.uk

Report Smuggling: customs.hotline@hmrc.gsi.gov.uk