A secretive think tank which called for the NHS to be scrapped while its heads pour millions into the Conservative Party – and its MPs’ – coffers is being funded by big tobacco, an investigation has found.

British American Tobacco is one of the groups funding the Institute of Economic Affairs (IEA), a free market think tank which is notoriously close-lipped about its donors.

The IEA has been an outspoken critic of public health measures for tackling smoking, obesity and harmful drinking, and past funders include organisations affiliated with gambling, alcohol, sugar and soft drinks industries.

Health experts said the findings, in the British Medical Journal (BMJ), raise the prospect of a future Conservative leader aligning with big business at the expense of the public’s health.

The IEA has dubbed the NHS one of the most “inefficient and overrated health systems in the world” and a 2016 report argued for a private health insurance model in the UK with top-up payments.

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It has close links to the Conservative Party and the chair of its board of trustees, Neil Record, donated £32,000 to health secretary Matt Hancock between 2010 and 2018.

Dominic Raab – who, alongside Mr Hancock, is aiming to succeed Theresa May as Conservative leader – also has close links with the IEA, speaking at its 60th anniversary event, and promoting an annual essay competition as recently as last month.

When asked about these links by the BMJ, a spokesperson said Mr Raab has “always been a strong supporter of public health initiatives to make the UK healthier and reduce pressures on the NHS”.

While Mr Hancock is among the biggest beneficiaries, 30 Tory MPs including David Davis, Liam Fox and David Willets have received cash or hospitality from Mr Record or fellow trustee Sir Michael Hintze.

In total MPs have declared funding to the value of £166,000 from the pair since 2005, and they have donated £4.3m to the Conservative Party.

The BMJ investigation identified a 1999 document listing UK supporters of the IEA, including British American Tobacco, Rothmans UK Holdings, Tate and Lyle, Whitbread, and Coca-Cola Great Britain and Ireland.

When the authors followed up with key organisations to see which were still actively funding the IEA, British American Tobacco confirmed it was still donating.

Professor Graham MacGregor, founder of the charities Action on Sugar and Action on Salt, said the prospect of a government following the IEA’s lead was “extremely concerning”.

Ian Gilmore, chair of Alcohol Health Alliance UK, said: “Public health would be an early victim of populist free marketism and the victims would be the most vulnerable – including children.”

Funding cuts have already created a “public health crisis”, Mr Gilmore said. “Shrinking the state would make this even worse.”

The IEA said the report predates its current senior staff by a decade and said the BMJ does not have a monopoly on the health and lifestyle economics debate.

“The report also implies that the IEA funds – directly and indirectly – members of parliament,” it added in a statement. “The IEA talks to MPs across the political spectrum, as do all other think tanks. This isn’t a ‘funding link’. The IEA does not give money to any political efforts, and we consider these suggestions to be slanderous.

“The BMJ’s insinuation is that we only purport a free market analyses because we are paid to. This is categorically untrue.”