• The time at which it is to be done must be defined; this could be expressed as a start date and end date (a fixed-term contract), or as a start date, with the work to continue until an agreed period of notice is given by either you or the other person (a subject-to-notice contract).

• The amount of money that the person you are engaging will get for the specified work must be clear. It may be a fixed price-for-the-job deal, or it may be an hourly, daily, weekly or monthly rate, with separate payments (which again must be clearly defined) for extra hours, unsocial hours, travel time, travel, subsistence and accommodation expenses and so on.

If your contract is not clear enough on these basic points, it could be legally "void for uncertainty of meaning". If it does not specify a payment (or some other reward such as the value to an interviewee of having his/her argument heard on television), it could be "void for lack of consideration". If you use the model contracts based on the industry agreements that you will find under the icons at the end of this page, you should be safe.

The written contract, which may be anything from an exchange of letters signed by both parties to one of the standard forms to a long and complex legal document, is the evidence of the terms of the agreement you have reached. It is always better to have that evidence in written form, but an oral contract is still binding,