Mezue ahịrịokwu na-esonụ: N'egwuregwu Olimpik Tokyo 2020, Duncan meriri ọlaọcha na 200m freestyle, na-agwụ 0.04 sekọnd n'azụ onye mmeri na onye otu ya, Tom Dean. Ọ gbasoro ya na ọla edo dị ka akụkụ nke 4 × 200m freestyle relay team na Tom Dean, James Guy, na Matt Richards, na-emeri ya na European ndekọ nke 6 nkeji 58.58 sekọnd. O nwetakwara ọlaọcha n'asọmpi 200m nke ụmụ nwoke, na nke ọzọ n'asọmpi 200m nke ụmụ nwoke.
4 × 100 mita medley relay na Luke Greenbank, Adam Peaty, na James Guy, na-eme ka ọ bụrụ onye egwuregwu bekee mbụ meriri ọla anọ n'otu egwuregwu na-eduga na oku maka ka a họpụta ya maka knighthood.