World Wide Web inventor Sir Tim Berners-Lee has said the impact of fake news is increasingly concerning, as he unveiled plans to tackle "unethical" political advertising and the harvesting of data.

The British computer scientist said, exactly 28 years after his invention, the three new trends have become alarming in the last 12 months.

In an open letter published on Sunday, Sir Tim, 61, said misuse of data has created a "chilling effect on free speech" and warned of "internet blind spots" that are corrupting democracy.

One problem, he wrote, is that most people find their news and information through a "handful" of social media sites and search engines, which are paid whenever someone clicks a link.