David Cameron announced on 13 July, that Britain should spend more of its defence budget on spy planes, drones and special forces to counter militants and Islamic State in Iraq and Syria

Earlier in July during the budget, the government said it would meet Nato's defence spending pledge of 2% of gross domestic product (GDP) for the next five years, which would boost budgets to £47.7bn ($74bn) a year by 2020.

Cameron said: ''It's about making sure we are safe in a very unstable and dangerous world, and because we have a strong economy we are able to make the commitment to spending more over and above inflation on defence, as much potentially as £6bn more between now and 2020.

"That will make sure Britain is safer, British people are safer and we defeat, for instance, the surge of Islamist extremism which is doing so much damage to our world and damage to our country."

The prime minister made the comment as he visited military personnel at RAF Coningsby in Lincolnshire and went to observe training exercises and equipment.

In a speech to servicemen and women, he promised to invest in equipment and special forces to combat Islamic extremists.

Cameron said: ''This is the threat of our generation. The battle of our generation. The fight we are going to have and I'm absolutely determined that the RAF, the army, the navy will have the equipment, the means, the resources to deal with this.

"One of the things that will mean is making sure we will have the drones, the spy planes, the special forces, the unique capabilities that make sure we can deal with this threat at its source."

Britain's defence chiefs will conclude a security review later in 2015.