EVENT 323 Men Open 400m Freestyle - Heats
| Heat Number - 1 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 3 | 2 | Harrison Shaw | 15 | | Flitwick | 4:35.60 |
| 4 | 4 | George Hooper | 15 | | Co St Albans | 4:33.76 |
| 5 | 3 | Charlie McKinnon | 15 | | St Felix Sch | 4:35.20 |
| 6 | 1 | Thomas Spelman | 15 | | Stowmarket | 4:36.21 |
| Heat Number - 2 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 6 | Nathan Birchenough | 15 | | St Felix Sch | 4:32.47 |
| 2 | 8 | Rio Rogers | 18 | S14 | Basildon Ph | 4:30.88 |
| 3 | 10 | Isaac Farrugia | 15 | | Basildon Ph | 4:29.20 |
| 4 | 12 | James Peacock | 16 | | Co Peterboro | 4:25.55 |
| 5 | 11 | Ashton Redhead | 15 | | teamipswich | 4:26.94 |
| 6 | 9 | Daniel Meier | 15 | | Modernian | 4:29.71 |
| 7 | 7 | Daniel Thompson | 15 | | Thurrock | 4:31.00 |
| 8 | 5 | Ben Howlett | 15 | | teamipswich | 4:32.59 |
| Heat Number - 3 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 14 | Jamie Joshua | 16 | | Hatfield | 4:23.91 |
| 2 | 16 | Jason Ho | 16 | | Hatfield | 4:22.54 |
| 3 | 18 | Daniel Clayton | 16 | | teamipswich | 4:21.44 |
| 4 | 20 | Ben Minister | 16 | | Thurrock | 4:20.52 |
| 5 | 19 | Roan Brennan | 16 | S9 | Basildon Ph | 4:20.63 |
| 6 | 17 | Sandijs Cecins | 15 | | Colchester | 4:21.60 |
| 7 | 15 | Daniel Moyses | 16 | | Co Peterboro | 4:23.49 |
| 8 | 13 | Patch Robinson | 15 | | teamipswich | 4:25.16 |
| Heat Number - 4 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 22 | Jago Derrington | 16 | | Bishop Stort | 4:19.52 |
| 2 | 24 | Harley West | 18 | | Thurrock | 4:17.00 |
| 3 | 26 | Ryan Wall | 15 | | Co Cambridge | 4:15.11 |
| 4 | 28 | Mark Milburn | 17 | | Colchester | 4:12.01 |
| 5 | 27 | William Ellard | 16 | | St Felix Sch | 4:14.85 |
| 6 | 25 | Flynn Ryan | 20 | | Co Cambridge | 4:15.76 |
| 7 | 23 | Thomas Ford | 16 | | Basildon Ph | 4:19.05 |
| 8 | 21 | Joe Power | 15 | | Basildon Ph | 4:20.52 |
| Heat Number - 5 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 30 | Jack Pallant | 18 | | Team Waveney | 4:09.34 |
| 2 | 32 | Matthew Baker | 16 | | West Suffolk | 4:07.30 |
| 3 | 34 | Marin De Villard | 17 | | St Felix Sch | 4:05.10 |
| 4 | 36 | Nathan Wells | 24 | | West Norfolk | 3:55.50 |
| 5 | 35 | Joe Cooper | 18 | | teamipswich | 3:58.20 |
| 6 | 33 | Matthew Wright | 24 | | Team Luton | 4:07.20 |
| 7 | 31 | James Speers | 19 | | Basildon Ph | 4:08.74 |
| 8 | 29 | Daniel McGuinness | 16 | | Basildon Ph | 4:10.08 |