When attending an interview do not leave anything to chance, by preparing thoroughly before hand you will be ready for whatever the dastardly interviewer chooses to throw at you, unless it is furniture in which case it is a safe bet to assume that you haven't got the job.

If you are to keep your cool even during the interview from hell, consider the following situations and think how you would react.

Deliberate attempts by the interviewer to crack your resolve

The interviewer brings in other colleagues to meet and question you unexpectedly during the interview.
When the new entrants to the room are introduced stand and shake their hands, smile, make eye contact, and greet them.

Resume your seat as before and listen to what they have to say and respond accordingly, try not to repeat information that you have already covered with the interviewer. You may want to make reference to what has already been said "I was just explaining to Mr Taylor that in my previous managerial position I…"

Try to pose questions to the new comers that are relevant to their role within the company.

Handle criticism of your CV
The interviewer may set about picking holes in your CV. Do not become defensive, take on board their criticisms and say why you did it a different way. They must have thought your CV was good enough or else you wouldn't have reached the interview stage.

Tough, aggressive questioning
The interviewer may pose a couple of deliberately spiked questions to see how you respond under pressure. Do not worry they are not going to shine a bright light in your eyes and ask, "what were you doing on the night of the 14th"? Take it easy, do not become defensive and reply in a considered way.

"I suppose in a couple of years time, you'll be wanting to get married and start a family?"

"For the foreseeable future my career is a greater priority than starting a family". If it is your intention to have children in the near future ask what provision the company could make for maternity leave, be positive and state that you would intend to return to work after the birth as soon as possible. Reply honestly.

"I see that you failed a few subjects in your degree, can you explain what happened"

If the reason for this academic lapse was due to excess beer drinking and partying it is probably best not to admit to this. Instead say something like "I found moving from A-Levels to Degree level to be a steeper transition than expected and it took me a while to adjust", if you feel inclined you can say that you failed because you were having "personal; problems" the interviewer will probably not enquire deeper. If the reason was due to worthwhile extra curricular activities encroaching on study time or sickness, then say so.

Unexpected tests
It is possible that when you arrive at the interview there will be a test set up for you, or a role playing exercise to take part in. Do not refuse to carry it out, just do your best. If you are asked if you need more time to finish, do not feel too proud to accept it. Take your time, accuracy is often more important than quantity of output.

Chance circumstances that could slip you up

The Interviewer may be having a bad day
Be patient, the interviewer may be very busy, do not be perturbed if they do not instantly know why you are visiting. They may be running late, if you have to wait for a long time use the bathroom facilities, flick though a newspaper, focus on what you want to say during the interview, perhaps chat to the receptionist.

The interviewer may be younger than yourself
If you are applying to an Internet firm or any new start-up business then it is conceivable that the employer will be your junior. If you are many years older, do not be offended if the interviewer shows little respect, and similarly you should not say anything patronising. It is best to forget it, and not to draw attention to the fact, for example do not say, "Ah, I remember when I was your age, this tower block was a green field, and I used to collect bottle caps for a crown a piece".

If the person supposed to be interviewing you is not available and someone else has to stand in
Do not let this phase you, there are many reasons why the original interviewer may not have been able to make it, for example due to Illness, a double diary booking, or an urgent appointment. Ask if it would be convenient for you to come back on another occasion, if they say that it is not necessary then go ahead with the interview with the same confidence and aplomb as you would any other.

Ask whom you should contact to follow up the interview, i.e. the original interviewer or the replacement.

You know one or the entire panel of interviewers
Ignore this fact, do not start calling people by their Christian names. Remain professional and answer their questions as if they had never met you before.

Badly prepared interviewers
Be patient and not critical of their incompetence.

Questions you don't know the answer to
It is better to say, "I'm sorry I don't know the answer to that question" rather than to 'Um and Ah' a lot and say a lot of rubbish.

Questions where you are asked to give an opinion
Give a balanced view, offering both sides of the argument. If you know what the company policy on the matter is, perhaps go with that, or if you can explain articulately why that is the wrong policy to adopt.

The feeling the interview outcome is already known
Do not let this effect your performance, you never know for sure what their decision will be.

Deciding during the course of the interview you are no longer interested in the job
Do not get up and leave, continue with the interview as you would if you wanted the job. If there is a specific problem you have that has changed your mind discuss it, perhaps there is a way around it?

Seeing another interviewee who you know
If you meet a friend in reception, exchange the time of day but do not be too chatty, in this environment they are the competition. Remain professional and wish them good luck with their interview.

Interviewers are not ogres, most of the time they are not trying to catch you out they simply want to get the best personnel for their company. If you stay cool and calm and follow these guidelines you won't go far wrong.