Jihadi John tops the list of targets for potential future RAF drone strikes in Syria, Whitehall sources have revealed.

The British Islamist fanatic, whose real name is Mohammed Emwazi, is infamous for beheading hostages in terrorist videos, including Scots aid worker David Haines. The 27-year-old is said to top a list of at least five terrorists with links to a London terror cell.

The UK Government believes Emwazi is in hiding, possibly near the Isis stronghold of Raqqah in northern Syria, where fellow jihadists Reyaad Khan, 21, from Cardiff and Ruhul Amin, 26, from Aberdeen were killed last month by a UK drone strike.

David Cameron told MPs on Monday that Khan was masterminding “barbaric” terrorist attacks in Britain, including, it is thought, a Tunisia-style massacre at the VJ commemorations in London, which were attended by the Prime Minister and the Queen on August 15.

The prospect of more drone strikes in Syria has been raised by Michael Fallon, the Defence Secretary, who made clear the UK Government would “not hesitate” to undertake fresh attacks if a clear threat to British lives was identified.

He refused to be drawn on the number of terrorists planning attacks against Britain but said it was more than three.

"Government has a duty, where it has information and the ability to prevent such attacks…to deal with them,” explained Mr Fallon.

But the drone strike – unprecedented in that it was a British strike against British citizens in a country with which Britain is not at war – has raised concerns the UK Government has crossed a line by sanctioning ex-judicial killings, which could be challenged in court.

No 10, which declined to comment on the suggestion Jihadi John tops a UK hit-list, revealed the meeting of senior members of the National Security Council, which approved the use of drones to target specific individuals in Syria, had taken place "some months ago".

The Attorney General's advice that the action was legal, on grounds of self-defence, had already been received by the time of the meeting, it added.

But the SNP and Labour demanded an inquiry into the RAF drone strike.

Angus Robertson, the Nationalist leader at Westminster, and Harriet Harman, Labour’s acting leader, called for Westminster’s Intelligence and Security Committee to investigate. It can summon intelligence chiefs to give evidence but a new committee has not yet been appointed following the General Election.

Alex Salmond, the SNP’s Foreign Affairs Spokesman, said the committee must be formed by the end of the month and the UK Government had to provide it with details of the criteria it used and the evidence it based the military strike on.

“Without that affirmation,” he argued, “they are on tricky ground in terms of the overall position.”

The MP for Gordon added: “There has to be a procedure – it’s not enough, with great respect to Michael Fallon, to say I think such and such – there has to be a lawful, proper procedure that satisfies legal requirements and democratic scrutiny.”

Elsewhere at Westminster, actress and UN envoy Angelina Jolie Pitt, told a House of Lords hearing that Isis was using rape as a “centre point of their terror”.

Calling for more action to tackle sexual violence in conflict areas, the Hollywood star told peers that Isis leaders were ordering militants to rape. "They are dictating it as policy; this is beyond what we have seen before...They are saying: 'you should do this, this is the way to build a society.'"

In a separate development, Bethany Haines, Mr Haines’s teenage daughter, said she approved of the UK drone strike, telling ITV News: “It is a step in the right direction but more direct action is needed.

"More strikes need to be carried out and not just on British jihadists but on Isis in general. I still think ground action is necessary and I hope it will be considered as a next step to wiping out Islamic State and their supposed caliphate," she added.

Rights Watch UK has begun legal action to force the Government into revealing the advice it received from lawyers justifying the killing of the British jihadists in Syria.