What is the function of an independent interpreter at an immigration and asylum interview?

It's to interpret. Independently.

The answer was in the question.

translation and to make sure that each side fully understand each other.

Technically there is no such thing. Our interpreters translate what you say and should do impartially. If you bring your own interpreter then s/he can verify the accuracy of the our translator but is obviously not independant since s/he is in your employ.

Technically they are there only to interpret and that is it. However in practice they abuse their position, provide opinion evidence to the Home Office and usually completely misleading information to the asylum applicant. They tend to regard themselves as experts and frankly in my 17 years experience in working with them I have most to be a hinderance. They are almost unregulated and frankly troublesome. However they are a necessary evil to assist communication. All too often they provide covert information to one or both sides and almost always this information is wrong. Their favourite tip is to suggest a theme to the asylum applicant for the interview by telling them that such and such a story always works or by introducing the asylum seeker to a so called 'great solicitor'. Usually they are receiving a 拢50 note from the solicitor for each such introduction and they also get the future interpreting work for the case off the lawyer.

Any advice you receive from such people should be reported to the Immigration Officer immediately and in writing. At that point the interview should terminate.

I am an immigration solicitor

Simply to interpret from one language to another. They are sometimes asked to transcribe statements so that the person concerned is able to sign a statement in his own language. The problem is that many of the languages used are not languages in which it is possible to secure the services of a properly trained interpreter who knows the rules of ethics and how to interpret from one language to another. The overall standard is patchy, to put it mildly!

In addition to the problems mentioned by Cyrus, there are reported to be cases of interpreters maliciously misrepresenting or misguiding applicants because of a political or ethnic enmity. Increasingly, interviews are now taped - one might have thought this would always have been the case, but frankly giving applicants an honest hearing has never seemed to be a Home Office priority.

Another problem is that interpreters claim competence in languages of which they only have limited knowledge.

If applicants suspect that there is a problem with the interpreter, they should not be afraid to indicate this as soon as possible directly to the interviewing officer if they can speak any English at all.