The results are reported by thousands of companies that use user data such as location and financial information to target ads.

According to one report, thousands of websites can use people’s sensitive data – from how they interacted with certain websites to their location and financial history – to serve targeted ads at any time.

This is the result of a study by the Demos think tank that we have shared exclusively with us. IIt is “almost incomprehensible” how much data about people is collected online, and that the collection of personal data is “difficult” and “time-consuming”.

“People have no control over their data or give meaningful consent to its use or the extent to which it is collected, while the purposes for which it is used remain unclear,” the report says.

The think tank said that “it is clear that the current privacy landscape is not working” and that companies and regulators need to “take their responsibilities seriously” to enforce privacy.

He urged the government to use the upcoming data protection bill due in the House of Commons on Monday and the Digital Markets Act to tighten data protection and launch public education campaigns to promote understanding of digital privacy.

The report involved five anonymous volunteers, aged 22 to 66, who were trying to find out how much data about them companies hold online.

One participant said he was “worried” and “worried” about the state of some companies’ data, while another was “appalled” by the assumptions his data made about him.

Social networking sites were among the main culprits, with one volunteer discovering that 2,242 companies could access their data through Facebook for advertising purposes.

Searches of their email history also revealed that between 72 and 231 companies were holding their personal information at any given time.

The data held by companies ranges from how users interact with certain websites to information about their location, financial history, shopping habits and personal preferences, and is often available to third party advertisers.

The report says some companies, including Experian, used de-identified financial data to create “profiles” that were then sold to companies to help them target specific customer groups.

A similar practice was followed by Amazon, which created “audience sets” that grouped users into categories based on their interests, which could then be used by advertisers on the site.

Volunteers found that getting companies to delete this data is “difficult, time-consuming, and not guaranteed to succeed.” One volunteer responded to 65 percent of their data deletion requests, while others only had 10 percent.

Demos said “stronger” data breach protection mechanisms, digital literacy public awareness campaigns and new standards for how websites use user data are needed.

Amazon, Meta and Experian have been contacted for comment.