Disclosure can be a minefield. The rule is simple - that the prosecutor must disclose to the defence all material relevant to the case. The problem with disclosure is that sometimes material discloses rather more than you might want, and the information disclosed may present challenges all of its own.

Often a complaint may be received that at first glance does not have prosecution written all over it. When it does become clear that prosecution may be the way to go, the file may have sustained collateral damage that may be difficult to deal with. The first damage to be sustained may be with correspondence, particularly where this passes through the hands of a number of people. Incoming letters will often have the date of receipt and a number written on them for post book purposes, but sometimes other information appears on them - the peremptory "see me" written by a senior officer who wants to know what is going on, or worse, some more obvious instruction "respond to this as a matter of urgency" or "is this matter still on-going?" - both instructions would have to remain on the letter and would be seen by the defence on the letter being disclosed. "See me" is easily dealt with - a responsible senior officer should want to know what progress has been made, but comments like the latter two invite defence comment. It is a cardinal sin to write on original correspondence - using sticky notes that can be removed is preferable unless you want the innermost thoughts of the person distributing the mail to feature in the case.

Disclosure of photographs has the potential to cause embarrassment. Generally, the prosecutor will be selective about which photographs are used, picking the ones in focus and showing issues relevant to the case. The defence, however, will wish to check all of the shots taken to ensure that those on which the prosecutor does not intend to rely would not be helpful to the defence case. This is not a problem when the remainder of the shots are of the premises or incident in question. It does, however, become a problem when the remainder of the shots are of the officers' children or domestic pets, inanely grinning clerical staff or worse, in the case of building control officers of my acquaintance, of the officers "mooning" at the camera. Hilarious at the time no doubt, but it is difficult to claim professional credibility in the face of such evidence. In such cases, less is more - either using the whole film, or where that is not possible, just rolling the film on and not taking the full number of exposures ensures that candid shots do not come back to haunt the photographer.

Officers' notebooks can contain potentially explosive stuff. Long boring stakeouts present opportunities for active minds and fertile imaginations to run riot. Harmless doodling rarely is - there is usually some underlying reason for the mind to be so occupied and a picture can sometimes speak a thousand words, none of them helpful. The relevant pages of officers' notebooks are disclosable, and if they feature less than flattering cartoons of the main players in the case, or a deep and undying affection for a football club, band or member of the opposite sex, they display a less than wholly focused attitude to the surveillance, which can lead to hard questions as to whether the officer was watching or was absorbed in their drawing at the critical point. Such questions probably will not bring the case to its knees, but they tend to suggest a less than professional attitude.

Internal office documentation must also be disclosed - the file note or the telephone message scribbled on whatever was to hand when the call was received are part of the case file and are therefore disclosable. I have seen file notes that contain relevant material alongside requests to pay lottery money and be at the leisure centre at a prescribed time to play five-a-side.

Such extraneous information is not damaging but an example I was quoted could have been. It seems that the officer taking the telephone message had crossed swords with the caller on a previous occasion, hence the message "SBFO rang" was understandable to the officer for whom the message was left. The translation - less than intelligent illegitimate person from O rang - would have to be provided to the defence, and it is unlikely that their reaction would be one of delight, even if they shared the stated view.

Anything that relates to a prosecution, or goes onto a case file has the potential to be disclosed. Therefore, officers should ensure that nothing other than relevant information is included. It is better to stifle creativity than to lose credibility.

Julie Barratt is director of CIEH Wales