A majority of the public, including Conservative voters, support tougher action against tax avoidance, according to an opinion poll after the revelations in the leaked Pandora Papers about widespread use of offshore tax havens by some of the world’s wealthiest people.

Among Conservative voters in the 2019 general election, 90% agreed that tax avoidance by large companies was “morally wrong even if legal”, the poll found.

That was higher than the figure for Labour voters, 85% of whom agreed. Support for the statement that tax avoidance by individuals is “morally wrong even if legal” was 87% among Conservative voters, 80% of Labour voters, and 81% of the public overall.

The poll, by Survation for the campaign group Tax Justice UK, followed reporting of the cache of files, named the Pandora Papers, leaked to the International Consortium of Investigative Journalists (ICIJ) and shared with the Guardian, BBC Panorama and international media partners. The largest ever such leak exposed the secret offshore holdings and finances of several wealthy donors to the Tory party, 35 world leaders, and more than 100 billionaires, celebrities and many other notable figures.

Several countries whose citizens were shown to own assets through offshore companies rapidly announced inquiries, but the British government has so far not responded robustly.

Tax Justice UK is calling for tax loopholes to be closed, such as the exclusion from stamp duty when properties are sold through offshore companies, under which Tony and Cherie Blair saved £312,000 in tax when they bought a London office in 2017. The group is also calling on the government to introduce a register identifying people who own UK property through offshore companies, promised by the former prime minister David Cameron in 2015 but which has still not been implemented.

The poll found 80% of people, including 83% of Conservative voters, agreed that the evidence of the Pandora Papers “makes me want to see tougher action against tax avoidance”.

Dame Margaret Hodge, chair of thecross-party parliamentary group on anti-corruption and responsible tax, said: “The Pandora Papers lifted the lid on a whole spectrum of immoral and illegal behaviours, including the very worst tax avoidance. Now this important polling from Tax Justice UK shows that people are well and truly fed up with tax dodging. What is striking is that it’s Tory voters who are most upset at this egregious conduct.

“It’s high time that Boris Johnson hears the outcry from his voters and finally takes action. The big corporations and rich individuals who shirk their responsibilities must be made to pay a fair share.’

The Treasury has been approached for comment.