The British government's support for US drone operations over Pakistan may involve acts of assisting murder or even war crimes, the high court heard on Tuesday.

In the first serious legal challenge in the English courts to the drones campaign, lawyers for a young Pakistani man whose father was killed by a strike from an unmanned aircraft are seeking to have the sharing of UK locational intelligence declared unlawful.

Noor Khan, 27, is said to live in constant fear of a repeat of the attack in North Waziristan in March last year that killed more than 40 other people, who are said to have gathered to discuss a local mining dispute.

The British government has declined to state whether or not its signals intelligence agency GCHQ passes information in support of the CIA drone operations over Pakistan, although the court heard that media reports suggest that it does.

The case opened as the RAF confirmed that it is to double the number of its own drones flying combat and surveillance operations over Afghanistan. The five additional aircraft will be operated from the UK for the first time, rather than the US. The UK's existing Reaper drones, which are used to target suspected insurgents in Helmand province, have been operated from Creech air force base in Nevada because the RAF has not had the capability to fly them from Britain.

Martin Chamberlain, counsel for Khan, said that a newspaper article in 2010 had reported that GCHQ was using telephone intercepts to provide the US authorities with locational intelligence on leading militants in Afghanistan and Pakistan. The report suggested that the Cheltenham-based agency was proud of this work, which was said to be "in strict accordance with the law".

On the contrary, Chamberlain said, any GCHQ official who passed locational intelligence to the CIA knowing or believing that it could be used to facilitate a drone strike would be committing a serious criminal offence.

"The participation of a UK intelligence official in US drone strikes, by passing intelligence, may amount to the offence of encouraging or assisting murder," he said. Alternatively, it could amount to a war crime or a crime against humanity, he added.

Chamberlain said that no GCHQ official would be able to mount a defence of combat immunity, but added that there was no wish in this case to convict any individual of a criminal offence. Rather, Khan was seeking a declaration by the civil courts that such intelligence-sharing is unlawful.

Between June 2004 and September this year, according to research by the Bureau of Investigative Journalism, drone strikes killed between 2,562 and 3,325 people in Pakistan, of whom between 474 and 881 were civilians, including 176 children.

With the number of drone strikes increasing sharply under the Obama administration, the London case is one of several being brought by legal activists around the world in an attempt to challenge their legality of the programme.

In Pakistan, lawyers and human rights activists are mounting two separate court claims: one is intended to trigger a criminal investigation into the actions of two former CIA officials, while the second is seeking a declaration that the strikes amount to acts of war, in order to pressurise the Pakistani air force into shooting down drones operating in the country's airspace.

During the two-day hearing in London, lawyers for Khan are seeking permission for a full judicial review of the lawfulness of any British assistance for the US drone programme.

Lawyers for William Hague, the foreign secretary, say not only that they will neither confirm nor deny any intelligence-sharing activities in support of drone operations, but that it would be "prejudicial to the national interest" for them even to explain their understanding of the legal basis for any such activities.

For Khan and his lawyers to succeed, they say, the court would need to be satisfied that there is no international armed conflict in Pakistan, with the result that anyone involved in drone strikes was not immune from the criminal law, and that there had been no tacit approval for the strikes from the Pakistan government – another matter that the British government will neither confirm nor deny.

The court would also need to consider, and reject, the US government's own legal position: that drone strikes are acts of self-defence. It would also need to be satisfied that the handing over of intelligence amounted to participation in hostilities.

The government also says that Khan's claim would have a "significant impact" on the conduct of the UK's relations with both the US and Pakistan in an "acutely controversial, sensitive and important" area, and also impact on relations between the US and Pakistan.

The case continues.