Lawyers for the son of a victim of CIA drone strikes in Pakistan have written to Foreign Secretary William Hague wanting to know what the UK's policy is on providing intelligence for America's "targeted killing" campaign.
The CIA's drone programme in Pakistan, which is not publicly acknowledged by the United States, is hugely controversial.
The Pakistani authorities have criticised the attacks as violations of their country's sovereignty and international human rights campaigners have condemned reports of innocent civilian casualties.
American officials have privately said that the strikes have killed many Taliban and al Qaida commanders.
Leigh Day & Co, acting on behalf of Noor Khan, whose father was killed earlier this year in a drone strike on a jirga - or council of elders - in north-west Pakistan, have asked Mr Hague to answer questions on how far the UK assists the US in its drone strike programme.
The law firm said several reports have stated that British intelligence has provided locations for alleged militants targeted by the CIA's campaign.
Richard Stein, head of human rights at the firm, said: "This legal action simply looks to ask a number of questions of our Government regarding UK involvement in the drone strikes in Pakistan which, it is estimated, have killed thousands of people within a country we are not militarily engaged with and therefore, we believe, are against international law.
"We ask the Foreign Secretary whether any information is being passed by agents of the UK Government to US Government forces to assist in these attacks. Unless it is categorically denied that the UK continues to pass such information to the US Government forces, we require a clear policy statement of the arrangements which are in place and circumstances in which the UK considers it to be lawful to do so."
Clive Stafford Smith, director of legal action charity Reprieve, said: "CIA drone strikes are killing hundreds - if not thousands - of civilians and destabilising Pakistan. The British people have a right to know what their country's policy is regarding our involvement in this illegal and disastrous campaign."
A Foreign Office spokesman later said: "We will study this letter closely and respond to the issues raised."