Right-wing think tank the IEA received over half a million pounds from US-based donors since 2010.

A right-wing think tank that claims to produce independent research received over £578,000 from US-based donors since 2010.

The Institute of Economic Affairs (IEA) has received $742,000 (£578,760) in foreign donations channelled through a US non-profit named the American Friends of the IEA, according to official tax returns.

The returns show that the American Friends of the IEA issued a $188,000 donation in 2016, $166,000 in 2015, $175,000 in 2014, $82,000 in 2012, $52,000 in 2011 and $79,000 in 2010. While the returns are anonymised, each donation appears to have been made to just one “economic foundation” based in Europe. The returns contain no detail on the sources of this money, and no donation appears to have been made in 2013.

The documents also reveal that in 2016 the American Friends of the IEA was headed by Alejandro Chafuen and Bradley Lips, the former president and current chief executive of the Atlas Network of more than 475 right-wing think tanks.

It mirrors an arrangement used by IEA sister group the Taxpayers’ Alliance, which The Guardian has revealed was used to handle over $186,000 in donations. Both the Taxpayers’ Alliance and the IEA are members of the Atlas Network.

The tax returns reveal the scale of the IEA’s US funding as it faces two official investigations over allegations it offered potential US donors access to UK government ministers.

In a video obtained by The Guardian, IEA boss Mark Littlewood bragged that his think tank was in “the Brexit influencing game” and could connect donors with Conservative figures including Boris Johnson, Michael Gove and David Davis.

The IEA has been a vocal advocate of exploiting Brexit to boost US-UK trade, and in September worked with other right-wing think tanks to produce “a radical blueprint for a free trade deal between the UK and the US that would see the NHS opened to foreign competition, a bonfire of consumer and environmental regulations and freedom of movement between the two countries for workers”.

In another sign of the think tank’s closeness to Conservative figures and big money, The Red Roar has also revealed how trustees of the IEA donated £4.6 million to the Conservatives and in one case paid to dine with Theresa May.

The revelations have prompted calls for an inquiry into the funding of political non-profits and think tanks led by Shadow Chancellor John McDonnell.