Many interviews are straightforward conversations with a clear beginning, middle and end. However, there will be occasions when you could be caught out if you didn't keep your wits about you. Being aware of what might happen will ensure that you will never
be ambushed. Here's what I mean:
1) The silent assassin If there are two journalists in the studio (often a breakfast or drive-time show), only one will usually conduct the interview. The other may appear disinterested, looking at their notes, or listening to the producer in their earpiece. As you answer the last question and relax, the other journalist will spring to life, and say "just one more question on a different subject if I may". This is a favourite tactic of John Humphreys. You need to stay alert, otherwise you could fumble your answer.
2) The sand-filled sock You may be hit with a sudden heavily-weighted question right at the end of your interview. For example, it could include an assumption or assertion that is untrue, leaving you only a few seconds to respond. You must make sure that you deny any untrue accusation, even by just using the words "That's untrue", before delivering your brief core message.
3) The technical hitch You sail through the interview, deliver your message, and avoid any tricky questions. As you lean back to relax while the recording is being checked, you mention to the interviewer how glad you were not to be asked about THAT topic. A message comes through that the recording didn't work properly, and you need to do it all again. You can guess the first question.
4) The repeated question Michael Howard was asked the same question twelve times by Jeremy Paxman. Mr Howard refused to give a direct answer, but became increasingly uneasy. What should you do in a similar position? Relax. Smile. Stick to your core message. Better still, respond with a question of your own - "What would you do if..."
5) The downright insult Ignore it or swiftly dismiss it. Jeremy Paxman's final question to Chloe Smith, Treasury Minister, a few weeks ago was "Do you ever think you are incompetent?" She replied: "I think it is valuable to help real people in this way and I do think that is valued by people who drive.". Her answer should have been one word. "No".
The moral of all this, of course, is never to relax until you're safe at home. And get some training, of course.