A landmark ruling in 2003 challenged long-held assumptions about what constituted personal data. Michael Durant's case against the Financial Services Authority resulted in the courts defining personal data very narrowly, so that data became personal only in certain circumstances.
While only a court can rule on what the definition in the DPA really means, guidance from the ICO is influential. The ICO has now replaced its initial guidance on the implications of the Durant judgment.
"We have been aware for some time of the need to replace our guidance on the implications of the Durant judgment," said an ICO statement. "Inevitably that guidance reflected the fact that the Court of Appeal was widely understood to have adopted a rather narrower interpretation of 'personal data' and 'relevant filing system' than most practitioners and experts had followed previously. We recognised the need to produce guidance with a greater emphasis on what is covered than what is not."
The DPA defines personal data as "data which relate to a living individual who can be identified (a) from those data, or (b) from those data and other information which is in the possession of, or is likely to come into the possession of, the data controller, and includes any expression of opinion about the individual and any indication of the intentions of the data controller or any other person in respect of the individual".
It is the interpretation of that definition that is the subject of the ICO guidance. Knowing what is and what is not personal data is vital because the DPA's rules apply only to the processing of personal data.
The says in its new guidance that many kinds of information can count as personal data, even in situations in which people may not consider it to be so. It said, for example, that information could count as personal data even if it does not include a person's name.
"There will be circumstances where the data you hold enables you to identify an individual whose name you do not know and you may never intend to discover," said the guidance. "Similarly, a combination of data about gender, age, and grade or salary may well enable you to identify a particular employee even without a name or job title."
The ICO said that it was important to bear in mind that a person trying to identify another person might work quite hard to identify that person. Definitions of personal data, then, must be allowed to be quite wide in some cases, it said.
"When considering identifiability it should be assumed that you are not looking just at the means reasonably likely to be used by the ordinary man in the street, but also the means that are likely to be used by a determined person with a particular reason to want to identify individuals," the ICO said. "Examples would include investigative journalists, estranged partners, stalkers, or industrial spies."
The Office also said that a decision must be revised on occasion, and it must not be assumed that any decision on personal data is final. "Means of identifying individuals that are feasible and cost-effective, and are therefore likely to be used, will change over time. If you decide that the data you hold does not allow the identification of individuals, you should review that decision regularly in light of new technology or security developments or changes to the public availability of certain records," said the ICO.
The situation is complicated further by the fact that some information can count as personal data in one person's hands, but not in another's. The guidance gives the example of two near-identical photographs of a street party, one taken by a policeman, the other by a journalist.
"The data in the electronic image taken by the journalist is unlikely to contain personal data about individuals in the crowd as it is not being processed to learn anything about a identifiable individual," it said. "However, the photo taken by the police officer may well contain personal data about individuals as the photo is taken for the purpose of recording the actions of individuals who the police would seek to identify, if there is any trouble, so they can take action against them."
It also said that parts of documents can count as personal data without the whole document counting as such.
In the case involving Michael Durant he sought information held on him by the Financial Services Authority. The Court of Appeal ruled that just because a document contained his name it was not necessarily defined as personal data. This changed the perception of how wide a definition of personal data could be.
A more recent case turned on the issue of personal data. A researcher at the Scottish Parliament requested figures about childhood leukaemia in a defined area and was turned down because the information was seen as personal data. The House of Lords has been asked to clarify whether or not the information, which will not name any children, can count as personal data.
The ICO says that it will issue guidance on the meaning of "relevant filing system" – another key part of the Durant case – in the near future.