The Government is to recruit 1,900 security and intelligence agents and double spending on aviation security in response to the terror threat from Islamic State.

The announcement was made by Prime Minister David Cameron at the G20 summit in Turkey, which is taking place in the shadow of Friday night's slaughter in Paris and the downing of a Russian jetliner over Egypt - both of which have been blamed on IS.

Mr Cameron has also ordered a rapid review of security at key overseas airports amid a growing conviction that the Metrojet Airbus was brought down by a bomb planted in its hold at Sharm el-Sheikh.

He said the UK was engaged in a "generational struggle" against extremist terror. The additional spending will help "combat those who would destroy us and our values" and allow Britons to "continue with our way of life we hold so dear".

The struggle against IS will also be discussed in face-to-face talks between Mr Cameron and Vladimir Putin - their first meeting since the Russian president launched air strikes in Syria.

Measures to boost counter-terrorism and aviation security, to be detailed in the Government's five-year Strategic Defence and Security Review on November 23, include: :: A 15% increase in the 12,700-strong staff of the security and intelligence agencies MI5, MI6 and GCHQ with the recruitment of an additional 1,900 personnel :: At least a doubling in the £9 million annual spend on aviation security :: Additional aviation security experts to provide regular assessments of airports around the world - with a focus on locations used by large numbers of British travellers :: Procedures to enable a "surge" of security experts to respond to incidents like the Sinai crash :: More advice, training and equipment for other countries to increase security at airports :: Increased research into screening technology and the detection of new threats The plan is expected to be endorsed at a meeting of the National Security Council chaired by the PM in Downing Street on Tuesday.

Number 10 said Mr Cameron had ordered a "step change" in the UK's approach to aviation security. Following the scare which saw flights from Sharm el-Sheikh suspended last week, UK specialists will conduct assessments at airports around the world over the next two months.

Inspections will focus on the nature and scale of the threat, physical security at airports and measures for passenger and baggage screening. Priority will be given to locations in the Middle East and north Africa favoured by British tourists.

French President Francois Hollande was absent from the annual gathering of 20 leading world economies, as he remained in Paris to lead his country's response to the attacks. France was represented by foreign minister Laurent Fabius.

The Prime Minister is expected to address the terror threat in a speech to the Lord Mayor's banquet in the City of London on Monday evening.

He will spell out his determination to devote some of the proceeds of the UK's recent economic growth to boosting security in the wake of attacks in Paris, Egypt, Belgium and Tunisia.

Speaking ahead of his address, Mr Cameron said: "I am determined to prioritise the resources we need to combat the terrorist threat because protecting the British people is my number one duty as Prime Minister.

"Our intelligence agencies work round the clock behind the scenes and as the threat has grown so they too have risen to the challenge. Much of what they do cannot be seen by us or talked about but their courageous and determined efforts allow us to go about our daily life.

"This is a generational struggle that demands we provide more manpower to combat those who would destroy us and our values."

He added: "We will also step up our efforts on aviation security, helping countries around the world to put in place the tightest security measures possible so that we can continue to enjoy places like Egypt and Tunisia and continue with our way of life we hold so dear."