A man claiming to represent the ousted Taliban regime said it was responsible for the attack in the provincial district of Girishk. He said all eight Afghan soldiers had been killed.
There are regular clashes in Helmand, which is Afghanistan's top opium-producing area.
More than 40 people were killed there earlier this month in a single day of clashes between suspected Taliban fighters and Afghan security forces.
More than 3,000 British troops are soon due to be based in Helmand Province as part of a plan to expand the NATO-led International Security Assistance Force (ISAF) from 9,000 to about 16,000 troops this summer.