Data collected by Essex County Council's website is being used by several companies to profile its users.

The authority is among many to collect visitors' data through advertising cookies – small text files – to track how people use its websites, including which sections users visit the most.

But although the data is anonymous, meaning advertisers do not know personal information like names and addresses, the information may subsequently impact people’s online profile.

Data collectors discovered by browser company Brave on the county council’s website include one real time bidding company that shares visitors’ data with a large number of companies every time the page is loaded.

The Information Commissioner’s Office has said the adtech industry appears “immature” in its understanding of data protection requirements and has general concerns around the level of compliance of real time bidding.

This includes where the processing of “non-special category” data is taking place unlawfully at the point of collection.

“Our findings show that councils are exposing the people of the UK to mass profiling. This is dangerous, because it leads to manipulation and discrimination”, said Dr Johnny Ryan, chief policy officer at Brave.

“This is a problem when an algorithm decides to not shortlist your application for a job based on your previous activity on a council’s drugs support page, for example.

“Once your interests and online activity is out in the wild you have no idea how it might be used.”

An Essex County Council spokesperson said: “Our website engineers are aware of the issues surrounding data tracking and will always act to comply with government guidance.”