The British are just as equally as responsible for friendly fire incidents in Afghanistan. More British soldiers were shot by their own side than the Americans. The reason why Americans have more friendly fire incidents because we did most of the work there than 25 NATO nations combined. The USAF and the USN provided more air support to the allies than all 25 NATO nations combined, therefore friendly fire incidents will likely occur among the US.
The U.S. has been responsible for 4 British military deaths in Afghanistan/Iraq:
Iraq - March 23 2003: A U.S. Patriot missile shot down a British Panavia Tornado GR.4A of No. 13 Squadron RAF, killing the pilot and navigator. Investigations showed that the Tornado's identification friend or foe indicator had malfunctioned and hence it was not identified as a friendly aircraft. Therefore, a faulty maintenance and equipment failure caused it, not the U.S. so who's to blame?
Iraq - March 28, 2003: A pair of U.S. A-10s from 190th attacked 4 British armored reconnaissance vehicles of the Blues and Royals, killing 1 and injuring 5.
Afghanistan - 5 Dec 2006: An F/A-18C on a Close Air Support mission in Helmand Province mistakenly attacked a trench where British Royal Marines were dug-in during a 10-hour battle with Taliban fighters, killing 1 Royal Marine.
The British have been responsible for 15 British military deaths in Afghanistan/Iraq:
Iraq - March 30 2003: Royal Engineers killed a Royal Marine Chris Maddison when his river patrol boat was hit by a Milan Missile after wrongly identified as an enemy vessel in Al-Faw Peninsula.
Iraq - March 26 2003: A British Challenger 2 tank came under fire from another British tank in a nighttime firefight. The turret was blown off and 2 crew members were killed.
Afghanistan - Jan 15, 2007: L.Cpls. Ford, Zulu Company of 45 Commando Royal Marines, died after receiving a gunshot wound which was later found to be due to FF. The final inquest has ruled he died from a Royal Marine machine gun bullet. The report added there was no "negligence" by the gunman, who had made a "momentary error of judgment".
Afghanistan - Dec 20 2009: A Royal Military Police Officer Michael David Pritchard was killed by a British Sniper while on observation post.
Afghanistan - Aug 23 2007: A U.S. F-15 called in to support British forces dropped a bomb on those forces due to wrong coordinates given to the pilot by a British Forward Air Controller. 3 privates of 1st Battalion, Royal Anglian Regiment, were killed and 2 others were injured. A British FAC is now facing manslaughter charges. There is no way you can blame the U.S. for this one. The wrong coordinates were given to a U.S. pilot by a British FAC.
Afghanistan - Jan 14 2009: Captain Tom Sawyer, age 26, of 29 Commando Royal Artillery, and Corporal Danny Winter, age 28, of 45 Commando Royal Marines, were killed when they were hit by a Javelin anti-tank missile fired in error by British troops in Gereshk, Helmand province, in southern Afghanistan.
Iraq - Fusilier Kelan Turrington, of the 1st Battalion, Royal Regiment of Fusiliers, was killed by machine-gun fire from a British tank.
Iraq - During a raid on 16 July 2006 to apprehend a key terrorist leader and accomplice in a suburb of North Basra, Cpl John Cosby, of the Devonshire and Dorset Regiment, was killed by a 5.56 mm round from a British-issued SA80. It was ruled to be a case of friendly fire by the coroner. It was reported that the British forces who shot him were unclear about the rules of engagement.
Afghanistan - A British female soldier and a Royal Marine was mistakenly killed by another British unit on patrol after her unit opened fire on an Afghan policeman assuming he was a Taliban insurgent. The British unit who killed a female soldier and a Royal Marine assumed they were under attack after the firing happened.
Afghanistan - Sapper Mark Antony Smith, age 26, of the 36 Engineer Regiment, Royal Engineers, was killed by a smoke shell fired upon by British troops in Sangin Province, Afghanistan. The MoD is investigating his death and said a smoke shell, designed to provide cover for soldiers working on the ground, may have fallen short of its intended target.
Afghanistan - In Sangin Province, an RAF Harrier mistakenly strafed British troops missing the enemy by 200 metres during a firefight with the Taliban on 20 August 2006. This angered British Major James Loden of 3 PARA, who in a leaked email called the RAF, "Completely incompetent and utterly, utterly useless in protecting ground troops in Afghanistan".
Afghanistan - On 9 July 2008, nine British soldiers from the 2nd Battalion, The Parachute Regiment were injured after being fired upon by the British Army Westland WAH-64 Apache helicopter while on patrol in Afghanistan.