The influence exerted on the prime minister by his partner, Carrie Symonds, will be explored in court after permission was granted last week for a judicial review into how the government came to pull a cull on badgers in Derbyshire.

The case could embarrass Boris Johnson and raise questions about the government’s willingness to listen to its advisers when formulating policy.

Symonds, a passionate animal rights defender and a patron of the Conservative Animal Welfare Foundation, has, along with environment minister Zac Goldsmith, been a staunch critic of the cull that is operating in 10 counties.

Last autumn the environment secretary, Theresa Villiers, ordered Natural England to scrap a cull in Derbyshire, where badgers are being vaccinated against TB, a decision warmly endorsed by Symonds and Goldsmith. The decision came three weeks after Symonds was briefed by Dominic Dyer, head of the Badger Trust, which opposes the cull.

The farmers union, the NFU, believes this meeting played a key role in the government ignoring scientific advice in favour of retaining the cull and sought a judicial review to determine how the decision was reached.

Last week the High Court confirmed the judicial review could proceed, meaning the NFU’s lawyers will be able to examine in court the basis on which the government pulled the cull.

Last month the NFU vice-president, Stuart Roberts, said: “We think that what the secretary of state did is unlawful, and that is why we’re launching this legal challenge. Alongside the Derbyshire farmers, we’re asking the court to rule that the direction issued to Natural England should be overturned.

“It’s come to light that before the secretary of state made her decision, her expert veterinary and scientific advisers told her that a licence should be issued to the Derbyshire area, to prevent the spread of bovine TB. It remains our view that any policy decisions must be based on science and evidence.”

Villiers has confirmed that Downing Street was involved in the decision to pull the cull. Earlier this month she told the Farmers Guardian: “Certainly we engaged with No 10 on the decision on Derbyshire, yes.”

Villiers said that she was not given a specific “direction” by the prime minister’s office, but admitted a “conversation had taken place” about whether a cull was suitable in a zone where badgers were being vaccinated.

Dyer defended Symonds’ role in bringing the Derbyshire cull to Johnson’s attention. He told the Observer: “I relayed my concerns to the prime minister in an open letter on the need to stop the badger cull in Derbyshire and other counties and I am pleased to see that Carrie made sure this reached him in Downing Street.

“It is completely legitimate for the Badger Trust or any other organisation opposing the badger cull policy to seek to engage with the prime minister in this way, particularly on such a hugely controversial, costly and cruel policy.”

The government was expected by now to have published figures confirming that more than 40,000 badgers were shot last year in 43 cull zones. This would put the total number of badgers killed under the government cull policy since 2013 at more than 110,000. But the figures have yet to be released.

There is speculation that Goldsmith – who is now in the House of Lords – may be made environment secretary in an impending reshuffle.

If so, farmers’ groups may seek reassurances that the government remained committed to the cull, which they believe is a crucial weapon in restricting the spread of TB.

A Defra spokeswoman said: “We have been notified about this legal challenge and we cannot comment on ongoing judicial proceedings.Bovine TB remains one of the greatest animal health threats to the UK, and the decision to pause the cull programme in Derbyshire will let us look at how the cull and existing vaccination projects in that area have worked together.”