There are 2 options available to you:
(1) You should tell the UK Border Agency by writing to:
Evidence and Enquiry Unit
12th Floor (Long) CorridorXXXXXbr />Croydon
You should state the individual's full name (as recorded in her passport) and date of birth, and (if you know it) her entry clearance or UK Border Agency reference number.
UKBA may curtail (cancel) the individual's permission to stay in the United Kingdom.
However, this will not automatically happen if the basis of his/her stay has changed - for example, she may qualify for permission to remain on a different basis, or there may be other compassionate or relevant reasons why it would not be appropriate to curtail her stay.
Before taking any action, UKBA will ask for your permission to use the information you have given them. If they decide to curtail the individual's permission to stay, she will have a right of appeal, which means that she could remain in the United Kingdom for some time before UKBA can consider removing her.
(2) Additionally, since the individual is committing an immigration offence you can send UKBA information by email. The information that you provide will be passed on the a local immigration team in the appropriate part of the country. Where appropriate, they will investigate and take action. In order to help UKBA send the information quickly to the local immigration team closest to the offence you are reporting, you should put the specific place (for example, Croydon) or the postcode (for example, CR0) in the message's subject line or title. Please also try to give us as much information as possible about the offence, such as names and addresses. All personal information is treated as confidential. UKBA will not tell the person involved that you contacted them, but they will also not be able to tell you what action is taken as a result of your information. Email:[email protected]
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