EVENT 323 Open/Male 400m Freestyle - Heats
| Heat Number - 1 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 3 | 1 | Jacob Dessoy | 16 | S8 | Runnymede | 6:55.64 |
| 4 | 3 | Corey Hare | 18 | S14 | teamipswich | 4:39.90 |
| 5 | 2 | Mark Evens | 28 | S14 | Hitchin | 5:29.19 |
| Heat Number - 2 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 5 | Isaac Buchan | 15 | | Co Norwich | 4:33.83 |
| 2 | 7 | Jamie Wilson | 15 | | West Norfolk | 4:31.88 |
| 3 | 9 | Will Riley | 15 | | teamipswich | 4:30.75 |
| 4 | 11 | Adam O'Neal | 16 | | Bedford SS | 4:25.60 |
| 5 | 10 | Zak Fellows | 15 | | Co St Albans | 4:25.79 |
| 6 | 8 | Daniel De Filippo | 15 | | Flitwick | 4:30.80 |
| 7 | 6 | Lucas Day | 15 | | Rochford | 4:32.60 |
| 8 | 4 | Oliver Fenwick | 15 | | Team Luton | 4:34.35 |
| Heat Number - 3 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 13 | Daniel Williams | 16 | | Hatfield | 4:23.61 |
| 2 | 15 | Ben Davison | 19 | | Hatfield | 4:22.12 |
| 3 | 17 | Reece Burns | 16 | | Chelmsford | 4:21.66 |
| 4 | 19 | Isaac Farrugia | 17 | | Basildon Ph | 4:21.60 |
| 5 | 18 | Daniel Thompson | 17 | | Thurrock | 4:21.60 |
| 6 | 16 | Oscar Hunter | 15 | | Norwich Swan | 4:22.00 |
| 7 | 14 | George Carter | 16 | | Co Cambridge | 4:22.37 |
| 8 | 12 | Billy Mead | 19 | | Linslade | 4:23.94 |
| Heat Number - 4 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 21 | Kian Lee | 16 | | Co Peterboro | 4:19.80 |
| 2 | 23 | Daniel Meier | 17 | | Biggleswade | 4:19.06 |
| 3 | 25 | Conor Mint | 15 | | Basildon Ph | 4:18.91 |
| 4 | 27 | Max Arnold | 18 | | Harlow Pen | 4:18.76 |
| 5 | 26 | Timon Chapman | 22 | | Norwich Swan | 4:18.85 |
| 6 | 24 | Jack Abram | 19 | | Co Norwich | 4:19.00 |
| 7 | 22 | Thomas Ford | 18 | | Basildon Ph | 4:19.16 |
| 8 | 20 | Dylan Davenport | 15 | | Bishop Stort | 4:21.54 |
| Heat Number - 5 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 29 | Luke Martell | 18 | | Watford SC | 4:18.50 |
| 2 | 31 | Benjamin Every | 16 | | St Felix Sch | 4:16.93 |
| 3 | 33 | Robert Fenner | 16 | | Basildon Ph | 4:15.56 |
| 4 | 35 | George Hooper | 17 | | Co St Albans | 4:14.79 |
| 5 | 34 | Daniel Moyses | 18 | | Co Peterboro | 4:15.00 |
| 6 | 32 | Jack Barnard | 19 | | Watford SC | 4:16.36 |
| 7 | 30 | Charlie McKinnon | 17 | | St Felix Sch | 4:18.06 |
| 8 | 28 | B Macdonald-Williams | 16 | | Bishop Stort | 4:18.65 |
| Heat Number - 6 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 37 | Harrison Shaw | 17 | | Flitwick | 4:10.42 |
| 2 | 39 | Jacques Bonsell | 25 | | Co Cambridge | 4:08.00 |
| 3 | 41 | Ryan Wall | 17 | | Co Cambridge | 4:06.04 |
| 4 | 43 | Daniel McGuinness | 18 | | Basildon Ph | 4:05.64 |
| 5 | 42 | Daniel Belsey | 16 | | Hatfield | 4:05.83 |
| 6 | 40 | Patch Robinson | 17 | | teamipswich | 4:07.06 |
| 7 | 38 | Orlando Dearing | 16 | | Co Peterboro | 4:08.10 |
| 8 | 36 | Jack Swindale | 16 | | Co Peterboro | 4:10.67 |