The UK's Information Commissioner, Elizabeth Denham, has opened a formal investigation into the use of big data analysis during the Brexit referendum.

Denham has also written to all political parties warning them to follow data protection and processing rules as they apply to campaigning in the run-up to the General Election.

The ICO said in March it was looking at the data protection risks created by data analytics used for political purposes – and it has now decided that a formal probe is justified.

Use of analytics and social media targeting is playing a growing role in political campaigning. Profiling of individual voters on social media and targeting associated advertising is believed to have had a significant influence on the US election.

Denham said in a blog post: "This is a complex and rapidly evolving area of activity and the level of awareness among the public about how data analytics works, and how their personal data is collected, shared and used through such tools, is low. What is clear is that these tools have a significant potential impact on individuals' privacy. It is important that there is greater and genuine transparency about the use of such techniques to ensure that people have control over their own data and the law is upheld."

She added the probe will involve "deepening our current activity to explore practices deployed during the UK's EU Referendum campaign but potentially also in other campaigns.

"Given the transnational nature of data the investigation will involve exploring how companies operating internationally deploy such practices with impact or handling of data in the UK."

Denham noted this will be a complex investigation requiring co-operation from political parties, social media platforms and data analysis companies both within the UK and abroad. She promised it would be a high priority for the ICO and an update would be provided later in the year.

The timing of the announcement was not related to current General Election campaigning, but that all parties should follow existing data protection and privacy law.

Last month the Electoral Commission started an investigation into allegations that the Leave.EU campaign had accepted impermissible donations of services and failed to correctly complete its spending return. ®