The UK and US must do more to protect internet users' privacy, the inventor of the world wide web, Sir Tim Berners-Lee, has warned as a survey of online freedoms is released.

Berners-Lee warned that "a growing tide of surveillance and censorship" posed a threat to the future of democracy, even as more and more people were using the internet to expose wrongdoing.

His remarks came before the second annual release of a global league table that classifies countries according to a set of freedoms. Since last year, the US has dropped from second place to fourth, while the UK has remained in third place. Sweden still tops the list, with Norway in second place. All of the Scandinavian countries – Sweden, Denmark and Norway – feature in the top 10.

The UK was poorly placed on privacy rights but was lifted by its high scores for availability of relevant content and the internet's political impact.

The table is compiled by comparing 81 countries, combining measures such as the extent of access to the internet, how much censorship is employed, and how "empowered" people are by its availability. The list has been expanded from the 61 countries surveyed last year.

Last year, Berners-Lee introduced the inaugural index by pointing out that there was no off switch for the internet – a fact that was proving uncomfortable for a number of governments that had tried to shut down radical dissent in the previous 12 months through the Arab spring.

But this year his remarks focused more on the threat of surveillance, which has been highlighted by the Guardian's revelations about the extent of online spying and subversion of internet protocols by the US's National Security Agency and the UK's GCHQ.

The survey found that 76 of the 81 countries examined did not meet "best practice" standards for checks and balances on government interception of electronic communications.

Speaking before an event to launch the updated version of the index, the 58-year-old British computer scientist said: "One of the most encouraging findings of this year's Web Index is how the web and social media are increasingly spurring people to organise, take action and try to expose wrongdoing in every region of the world.

"But some governments are threatened by this, and a growing tide of surveillance and censorship now threatens the future of democracy.

"Bold steps are needed now to protect our fundamental rights to privacy and freedom of opinion and association online."

The survey also found that almost a third of countries surveyed block politically sensitive content.

Web innovators, experts and policymakers, including Berners-Lee and the Wikipedia chief Jimmy Wales, were gathering in London on Friday to assess the World Wide Web Foundation's independent annual measure of the web's impact.

The US was the best performer this year on use of the web for social, political, environmental and economic empowerment, but received mediocre scores on the breadth of internet access, communications infrastructure, and for its lack of adequate safeguards to protect users' privacy from extensive electronic surveillance.

The Web Index Report revealed that beyond the digital divide, the world faces a growing "participation divide", as unequal access to knowledge and speech online denies millions the necessary tools for free and informed participation in democracy.

Wealthier groups in most countries were increasingly using the web and social media to gain knowledge and amplify their voice in public debate, the research suggested. Yet wealth was not necessarily a guide to success: Qatar, the world's richest country, ranked below Jamaica, Kazakhstan and Indonesia. Switzerland, the world's third richest country, ranked only just above Estonia.

But groups such as low-paid workers, smallholder farmers and women in the developing world were much less likely to be able to access vital information online.

Democratisation of information and communication flows was further constrained by a global trend towards greater online censorship and surveillance, the report warned.

Along with many other countries including the UK and US, Sweden's leading record in web innovation could be at risk from excessive state surveillance. Russia, meanwhile, ranked 41st, behind countries including the tiny island of Mauritius, for failing to have relevant content or offer empowerment to citizens.

Among emerging nations, Mexico achieved the highest overall position in the Web Index 2013, followed by Colombia, Brazil, Costa Rica and South Africa.

The Philippines was the developing country that achieved the highest overall ranking in the Web Index 2013, with high scores on web use and measurements of people using the internet and social networks compared with other developing countries. But that position may have literally been blown away by the typhoon that hit earlier this month, killing thousands and destroying connections between the islands.

However, except for Morocco (ranked 54th overall in the index), none of the developing countries in the Web Index achieved the UN World Summit on the Information Society target of connecting at least 50% of their populations. In Africa, fewer than one in five people were using the internet.

Anne Jellema, the chief executive of the World Wide Web Foundation, said: "Ten years after world leaders committed to harnessing technology to build an inclusive information society, parents in 48% of countries can't use the web to compare school performance and budgets, women in over 60% of countries can't use the web to help them make informed choices about their bodies, and over half the population in developing countries can't use the web at all.

"Countries should accelerate action to make the web affordable, accessible and relevant to all groups in society, as they promised at the World Summit on the Information Society in 2003."