GOV.UK
Working the examination: Ensuring clarity in your request for third party information
You should be as specific as possible when listing what you want to see. It is important that the third party should be clear about what it is you have asked them to provide, not only is this good customer service, but it will make it easier for you to judge whether they have complied, and to identify any gaps.
You should use your judgement in deciding how much time to allow for the third party to supply the information, taking into account the nature and volume of the information, but the period should never be shorter than 21 days from the date the notice is sent. Always be specific, don’t ask for information “within 21 days”, but say “by 19/5/2004”, etc.