Britain’s four-strong team of Kathleen Dawson, Peaty, James Guy and Anna Hopkin touched in 3:37.58s to break the previous 3:38.41s mark set by China in Qingdao last year.

The Chinese were second in 3:38.86s and Australia third in 3:38.95s.

The Caeleb Dressel-led US were relegated to fifth.

The mixed relay was one of three swimming events debuting in Japan along with the men’s 800m freestyle and women’s 1,500m freestyle.

Teams comprised two women and two men, with each of the four swimmers allocated to one of the four traditional medley strokes – backstroke, breaststroke, butterfly and freestyle.

Britain chose to lead off with Dawson, up against American backstroke giant Ryan Murphy and Australia’s Kaylee McKeown, who won the 200m individual title minutes earlier.

Peaty, who won 100m breaststroke gold in Tokyo, then took up the baton.

Guy swam a storming butterfly leg to hand over to Hopkin, who brought it home ahead of China’s Yang Junxuan, Australian 100m freestyle champion Emma McKeon and a chasing Dressel.