What length of clip from TV hosted online would constitute fair use under UK law?

I've been asked to make up a video to be hosted online (youtube or institution's own website) featuring another member of staff being interviewed at length on a TV News programme. Take the supplied DVD-VR, rip video stream, convert, upload, ho hum, not hard.

But, these requests are starting to become more common (from TV recordings and the odd published documentary DVD), and I'm wondering what kind of legal status these videos come under? As I'm in the UK it doesn't seem USA-style "fair use" entirely applies, but having done some quick searches I'm not seeing much firm answers either way. As most of them are single clips showing a certain item or excerpt from a longer piece for the purposes of example or promotion (in this case, what we and certain members of staff have to offer to clients, and their various areas of expertise that are high profile enough to get them on TV and specialist DVDs reasonably often), and generally less than 5 minutes long except for the latest one, I'm hoping it will be treated with some freedom and leniency, the same as photocopying a single chapter from a textbook in the library. However, while I'm going ahead with getting the thing converted, it'd be nice to get the legal truths pinned down - can anyone advise on this front?

Thanks :)