In many cases, success in libel actions depends on having the evidence to prove the allegations that have been made. Evidence can take many forms and the rules of evidence are complicated. What may seem to be strong, cogent evidence of a particular fact may be inadmissible when it comes to the court case. Witnesses may turn out to be unreliable, have an 'axe to grind' or be simply dishonest. The fact that the story has been written elsewhere, for example in other press articles, may suggest that it is true, particularly if no legal action has been taken over those articles. However, press articles are not admissible evidence in court of the truth of what has been printed. In addition, be very careful about relying on information found on the internet.

Since we may well have to prove the truth of allegations being made in programmes at some later date, it is essential that all evidence, for example statements from witnesses, documents, journalists' notebooks, contemporaneous notes of phone calls, are retained. As a matter of good practice, since material such as rushes and notebooks may need to be disclosed, any pejorative comments or comments which could be open to a hostile interpretation should be avoided. In court, programme-makers may well be cross-examined on what they have written in their notebooks or said while the camera is running.