Peers said that the ERG “paper on trade and the WTO suffers from some exceptionally basic errors of fact, which are unfortunately used as the basis for unfounded claims that could, if policy was based on them, significantly damage UK exporters”.

A Tory backbencher shown the ERG research by openDemocracy said that “if you needed proof that the ERG was a party within a party, this is it.

“This is the group that has encouraged many of the myths and fantasies about a hard and no-deal Brexit that are still influencing the policies likely to be road-tested by Boris Johnson in 10 Downing Street. Everyone is entitled to their opinion, but public money is being used to pay for this disruptive, often ill-informed dross.”

Spoon-fed talking points

The limited cache examined by IPSA reveals policy “lines to take” for ERG members, “possible questions” to ask ministers, and breakdowns of ministerial statements that in many cases accuse the government of masking Brexit’s “facts”.

ERG MPs were also given interpretations of key reports. These include a 2016 CBI report on the implications of Brexit which says 950,000 jobs could be lost by 2020, which was dismissed as a false forecast.

In a line that mirrors other anti-migrant rhetoric , the ERG research claimed “950,000 jobs are not lost” but rather these would be employment reductions in a post-Brexit UK economy because new jobs would no longer be created for EU migrants.

The CBI report estimated a post-Brexit GDP loss of between “£55 bn-£100bn by 2020”. ERG MPs were told the figure is simply a hypothetical “loss” based on a smaller population.

MPs attending debates were furnished with ERG “notes” questioning government facts which are described variously as “selective statistic picking” and “old rogue statistics”. The government was frequently accused of failing to “address the positives” and “distorting statistics”. On EU crime cooperation, the ERG said that the "Charter of Fundamental Rights makes it impossible to keep some undesirables out".

Prior to the 2016 referendum, ERG MPs were spoon-fed lists of questions for key government departments. MPs were told to ask questions on Foreign Office impartiality and whether Philip Hammond, then foreign secretary, believed the UK’s membership helped or hindered the UK in striking trade deals.

Talking Turkey

Questions on migration from Turkey, one of the key fears stoked by Leave campaigners during the referendum, are also suggested as a target. ERG members are told to ask Hammond if he “supports” Turkish accession to the EU, a move that few in Brussels think is likely to happen. ERG MPs were told they should quiz the Foreign Office on whether Turkish citizens should have Schengen visas and whether they should have automatic access to the UK.

In another 2016 ERG guide, MPs were encouraged to ask Theresa May, then home secretary, about Turkey, “free movement” for 80 million Turks and EU’s ability to negotiate a refugee deal with Turkey.