The British government on Friday rejected criticism of its intervention in Libya, arguing its involvement saved civilian lives and claiming the Islamic State group has been weakened in the country.

The government's comments follow a September report in which the parliamentary Foreign Affairs Committee published a damning assessment of the 2011 intervention alongside France.

The report said London's strategy was based on "erroneous assumptions and an incomplete understanding of the evidence," accusing the government of selectively taking the threats of dictator Moamer Kadhafi at face value.

But in its response the government argued its actions "undoubtedly" saved civilian lives in Libya.

"Qadhafi (Kadhafi) was unpredictable and had the means and motivation to carry out his threats. His actions could not be ignored, and required decisive and collective international action," the government said in its written response.

Kadhafi was ousted and killed during the uprising and Britain was criticised by the Foreign Affairs Committee for expanding its mission to protect civilians to a policy of regime change, a charge rejected by the government.

"Our objective remained clear at all times: to protect civilians and to promote stability in Libya," the government said, adding that it was "entirely appropriate" to target military sites after the Kadhafi regime failed to implement a ceasefire.

The 2011 bombing campaign came after Kadhafi loyalists pounded the eastern city of Benghazi, raising fears of an imminent massacre in the rebel stronghold.

Britain's then prime minister, David Cameron, was blamed in the report as "ultimately responsible for the failure to develop a coherent Libya strategy".

He declined to give evidence to the Foreign Affairs Committee, which heard from key players including former defence minister Liam Fox and former prime minister Tony Blair.

The government confirmed Blair had spoken to Kadhafi and said such efforts for a political solution "were unable to make progress", dismissing the Committee's claim that the government should have made better use of this direct line of communication.

Five years after the intervention, Libya is run by two rival administrations and remains embroiled in violence including the presence of extremists such as the Islamic State group.

The British government should have been aware that militant extremist groups would attempt to benefit from the rebellion, the Committee report said.

Defending its decision-making, the government said the vast majority of people opposed to Kadhafi were not linked to extremism and claimed the Islamic State was losing ground.

"Daesh are now on the back foot in Libya," the government said.