LONDON (Reuters) - Prime Minister Boris Johnson will address lawmakers on Monday about Britain's withdrawal from Afghanistan, amid criticism of the handling of the evacuation and failure to predict how quickly the Taliban would sweep through the country.

       The United States and Britain withdrew from Afghanistan last month, and Johnson's foreign minister Dominic Raab has admitted that both countries misjudged the Taliban's capacity to seize control. The Taliban took Kabul on Aug. 15.

       Johnson has faced stinging criticism from lawmakers for intelligence and leadership failures over the fall of Kabul, and he has admitted that the decision by the United States to withdraw left Britain with little choice but to pull its own forces.

       Some who served in Afghanistan have spoken of their anger and grief about what has happened, and Johnson will say that, despite the Taliban's rapid return, the efforts of a 20-year campaign were not in vain.

       "Thanks to their efforts, no terrorist attack against this country or any of our Western allies has been launched from Afghanistan for twenty years," Johnson will say in a speech to parliament when it returns from summer recess, according to extracts released by his office.

       "They fulfilled the first duty of the British armed forces - to keep our people safe."

       Johnson's office said that he would announce an additional 5 million pounds ($6.93 million) in funding for charities that offer support to veterans.

       ($1 = 0.7213 pounds)

       (Reporting by Alistair Smout; Editing by Emelia Sithole-Matarise)