Boris Johnson’s controversial enforcer, Dominic Cummings, an architect of Brexit and a fierce critic of Brussels, is co-owner of a farm that has received €250,000 (£235,000) in EU farming subsidies, the Observer can reveal.

The revelation is a potential embarrassment for the mastermind behind Johnson’s push to leave the EU by 31 October. Since being appointed as Johnson’s chief adviser, Cummings has presented the battle to leave the EU as one between the people and the politicians. He positions himself as an outsider who wants to demolish elites, end the “absurd subsidies” paid out by the EU and liberate the UK from its arcane rules and regulations.

But his critics say the revelation that Cummings has benefited from the system he intends to smash underscores how many British farmers are reliant on EU money that would evaporate if the UK leaves.

An Observer analysis of Land Registry documents and EU subsidy databases reveals that a farm in Durham, which Cummings jointly owns with his parents and another person, has received roughly €20,000 a year for most of the last two decades.

The revelation opens Cummings up to charges of hypocrisy, as writing on his blog, he has attacked the use of agricultural subsidies “dreamed up in the 1950s and 1960s” because they “raise prices for the poor to subsidise rich farmers while damaging agriculture in Africa”.

He notoriously came up with the claim that leaving the EU would allow the UK to spend an extra £350m a week on the NHS. His blog clarified the claim, explaining “the Treasury gross figure is slightly more than £350m of which we get back roughly half, though some of this is spent in absurd ways like subsidies for very rich landowners to do stupid things”.

Cummings came up with the claim that leaving the EU would allow the UK to spend an extra £350m a week on the NHS, a mainstay of the Leave campaign. Photograph: Paul Ellis/AFP/Getty Images

The website Farmsubsidy.org, which lists EU rural subsidies, reveals that the Durham farm received almost €208,000 between 2000 and 2009, roughly €20,000 a year.

The money was paid out to Cummings’s parents and another family member for several reasons including “set aside” – the now abolished and controversial scheme that paid farmers not to grow anything. The programme has been blamed for making it harder for food producers in developing countries to compete with their European counterparts.

A separate website, operated by the Department of Environment, Food and Rural Affairs, confirms further payments of roughly £6,500 each were made to Cummings’s parents “for practices beneficial for climate and environment” in 2017 and 2018.

And scrutiny of a third, offline database, reveals that subsidies worth nearly £19,000 were paid out in 2014.

The Liberal Democrats’ spokeswoman for young people, Layla Moran, said: “It shows sheer hypocrisy from Cummings that his farm has raked in hundreds of thousands from the ‘absurd subsidies’ he so often criticises.”

It is not clear when Cummings became the co-owner of the farm which his father reportedly bought after retiring from the oil industry. Land Registry searches show he was a co-owner in 2013. Reports suggest he moved to the farm in 2002, after leaving his job as the Conservative party’s director of strategy.

A profile of the Oxford-educated Cummings, for the Conservative Home website, explains that after quitting the post, “he then proceeded to spend two and a half years in a bunker he and his father built for him on their farm in Durham, reading science and history and trying to understand the world”.

His return to frontline politics has divided Tories. Some question whether his desire for Brexit comes at the expense of appreciating what may happen in key industries if EU structures and financial support disappear overnight.

Farmers have expressed their fears about what would happen to their sector. Last month, Helen Roberts of the National Sheep Association in Wales, said it would be “absolutely catastrophic” to leave with no deal and could lead to civil unrest among sheep farmers.

A Downing St spokeswoman declined to comment.