Thirty men, firing guns and mortars, attacked the convoy on Sunday in the Sangin district of the southern Helmand province. The patrol had found a weapons cache in the area. Earlier Afghan police reported 11 gunmen had been killed in the firefight.
"The coalition attacked the engaging enemy element as well as a second group attempting to reinforce the original group," said a military statement.
The military said two soldiers were wounded and airlifted to a medical facility, where they were in stable condition.
Four British troops have been killed in Sangin during the past week.
Also in Helmand province, Afghan police killed seven gunmen who attacked a police checkpoint in the Nawzad district, the interior ministry said. The police suffered no casualties, it said.
Enemy fighters left behind two bodies after the clash.
Elsewhere, a US helicopter crashed at Kandahar airfield, killing one pilot and wounding another.
The AH-64 Apache attack helicopter plunged to the ground shortly after taking off from the multinational force airfield while responding to a reported rocket attack on the base, a military statement said.
"The cause of the crash will be investigated, but we have ruled out enemy fire as a cause for the loss of the aircraft," it said.
In western Afghanistan, an explosion on Monday killed a teacher and wounded seven female students during an English class at Herat University.
The explosive device was planted in a rubbish bin. The Taliban oppose women receiving education and have bombed many schools and universities.
The commander of British forces in Afghanistan said he has asked for more equipment and suggested that he may ask for additional troops.
"In terms of force levels, we constantly keep those under review and I am confident that if I asked for more - and there are some requests which are in staff in process - London would listen to those requests," Brigadier Ed Butler said.
The NATO-led International Security Assistance Force, which includes British troops, is preparing to take over security from the US-led forces across the south of the country.