A senior commander has denied the British blocked an overhaul of the security arrangements at an Afghan base in the lead up to a Taliban attack in which two US marines were killed.
Two US generals were forced to retire in the wake of the attack last year at Camp Bastion - the main military base in Helmand province - in which eight American Harrier jump jets were destroyed.
Fifteen Taliban fighters dressed in American uniforms walked past an unmanned watchtower on to the airfield and opened fire with machine guns and rocket-propelled grenades.
One of the US generals subsequently told a Pentagon investigation into incident that the British ''knew that they had screwed up''.
Giving evidence to the Commons Defence Committee, Lieutenant General David Capewell, the Chief of Joint Operations, acknowledged that errors had been made but said they had not been "culpable errors".
He rejected claims the British - who had overall responsibility for security at the base - had blocked proposals by the Americans for a new memorandum of understanding governing the arrangements at the base.
He said that the joint UK-US executive steering group at the base had come forward with proposals earlier in the year following an attempted suicide attack on the runway where a plane carrying the then US defence secretary Leon Panetta had just landed.
However he said they had been "pushed back" by international force commanders at the Isaf headquarters in Kabul.
"You can see why in the range of balancing risk against reasons, on some occasions things were pushed back and rejected because there is not infinite resource. Judgments have to be made at the time about this," he said.
"People on the ground at the time would have determined to themselves that there are some shortcomings, they would have made judgments themselves about those shortcomings in the heat of battle and had a conversation about them with their higher headquarters.
"If their higher headquarters does not deliver them resolution to it, then what you have to do as a commander .... is adjust your own resources and and take risks in other places."