LOA, It is important to remember that the main purpose of the interview is to see if you "fit in" with the company and to check that the wonderful things you wrote on your CV were in fact done by you. Your qualifications and application are what got you to the interview stage.
I have interviewed literally hundreds of engineers and scientists for posts in a large research establishment and although scientists don't wear suits to work, they are standard dress for an interview. Think of an interview as a business meeting - that will give you an idea of the standards expected. Plus, you are out to create a good impression (I hope). Over the years I have seen several candidates who thought they were so brilliant that they should be hired in spite of a deliberate choice to come scruffy to an interview. I have never seen one of these candidates chosen.
Tips:
* Try to avoid anything that might "jar" with any member of the panel. Since you don't know their views and biases in advance you have to be conservative. Funny haircuts, visible tatoos, punctured ears, etc are out. Remember that the people interviewing you will be more senior and therefore probably older than you. The latest trend in not where you want to be.
* Check your appearance carefully before going in for the interview. Use the mirror in the gents. (Ladies don't need this advice, they always seem to get it right for interviews.)
* Carry a small reel of sellotape in your pocket. This is the quickest and easiest way to get fluff, hairs, etc off a dark suit in a hurry.
* Arrive in plenty of time and don't rush. Sweat pouring off your brow doesn't give the impression of someone in control of their life.
* Interviewers often ask questions at interview that either have no correct answer, or are so difficult that it is unlikely that anyone will be able to come up with a correct answer. These aren't asked to be sadistic. They are asked to separate the candidates who don't give up, when faced with difficulties. Never give up.
* Interviews often end with an opportunity for you to ask questions. If there is nothing you really want to know at that stage, it helps to have a sensible question prepared. Otherwise, the interview can end on a rather flat note.
* Re-read your CV the night before. Anything on your CV is fair game for interviewers questions. Candidates who don't seem to know what they put on their CV don't come over well.
Your original question was about clothing. Try and see it from the interviewers point of view.... If you can't make an effort for an interview, what are you likely to be like six months after you have been hired?
Finally, remember that the day of a successful interview is the best paid day of your life. The hours you spend preparing for the interview are vital.
Good Luck !