A recent visit to Washington DC by former Brexit secretary, David Davis, was funded by US business interests that want the UK to weaken its food and environment standards after it leaves the EU, Unearthed can reveal.

Davis visited the US in November 2018, together with former environment secretary Owen Paterson and the Institute of Economic Affairs’ (IEA) controversial trade expert, Shanker Singham, to discuss a post-Brexit US trade deal with the Trump administration.

The group met with senior trade and agriculture officials before travelling to Oklahoma to meet with its Lieutenant Governor, Todd Lamb, and visit agricultural research facilities at Oklahoma State University.

According to the register of MPs interests, funding for the trip was provided by several organisations, including the Institute of Economic Affairs and an Oklahoma business group called the E Foundation.

Earlier this year an undercover investigation by Unearthed found that the E Foundation had agreed to provide tens of thousands of dollars in funding to the Institute of Economic Affairs (IEA), with the aim of influencing Brexit.

Davis’ entry in the register reveals that the E Foundation paid £5,362 to cover the cost of his flights, accommodation and other expenses; while the IEA paid £1,949. The Chickasaw Nation, a Native American nation whose secretary of commerce, Bill Lance, sits on the E Foundation board of directors, also paid £4,052 to cover the cost of Davis’ flights.

Some of the costs of Paterson’s trip were also covered by the E Foundation and IEA – but the majority came from the Chickasaw Nation (£4,052) and UK2020, a think tank of which Paterson is the sole director (£4,933).

Paterson has frequently used his think tank, which does not disclose its sources of funding, to cover the costs of foreign trips.

Responding to the news, shadow cabinet office minister Jon Trickett told Unearthed: “The public must be wondering why on earth prominent MPs are being funded by opaque ‘charities’ to visit the US to discuss extreme free-trade deals.”

“They are entitled to answers. But to get them we will need to overhaul the way politics in this country works. The rules and regulations on funding, lobbying and transparency are simply not adequate to deal with the increasing complexity and global nature of the relationship between politics and big business,” Trickett continued.

Davis, Paterson and the E Foundation did not respond to requests for comment when contacted last week.

Really positive discussions on the future of UK/Oklahoma trade relationship. Sadly impossible to implement with the Draft Withdrawal Agreement as UK will not control its own tariffs or regulatory environment pic.twitter.com/pbhhjxbQ3M — Owen Paterson MP (@OwenPaterson) November 17, 2018

Very good meetings with USTR and with USDA on UK US trade deal but not possible on the current Withdrawal Agreement https://t.co/6OW5nomUzY — Shanker Singham (@ShankerASingham) November 16, 2018

It is at least the second time that Singham has met with US trade officials this year, according to documents obtained by Unearthed under US freedom of information rules.

A spokesperson for the IEA said: “Unearthed’s constant insinuation is that the IEA’s activities and publications only purport certain analysis and views because we are paid to. This is categorically untrue. If anyone really believes that IEA authors and spokespeople are socialist, tax-loving, big-state advocates at heart, who only advocate free-market economics for a pay check, then they are a) badly mistaken and b) we consider such accusations to be slanderous.”