EVENT 323 Open/Male 400m Freestyle - Heats
| Heat Number - 1 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 2 | 2 | Kian Ptolomey | 15 | | Putteridge | 4:34.87 |
| 3 | 4 | Lochlan Shaw | 15 | | Flitwick | 4:32.98 |
| 4 | 6 | Haiden Hall | 15 | | Deben | 4:31.12 |
| 5 | 5 | Corey Hare | 19 | S14 | teamipswich | 4:31.63 |
| 6 | 3 | Philip Spalding | 15 | | Putteridge | 4:33.63 |
| 7 | 1 | Jacob Dessoy | 17 | S8 | Runnymede | 6:25.99 |
| Heat Number - 2 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 8 | Tyler Stone | 15 | | Co Norwich | 4:29.10 |
| 2 | 10 | Ryan Wimpenny | 15 | | Cheshunt | 4:27.27 |
| 3 | 12 | Jamie Wilson | 16 | | West Norfolk | 4:25.68 |
| 4 | 14 | Daniel De Filippo | 16 | | Flitwick | 4:24.97 |
| 5 | 13 | Csanad Rehus | 16 | | Co Peterboro | 4:24.99 |
| 6 | 11 | Charlie Birdsall | 15 | | Co Cambridge | 4:26.25 |
| 7 | 9 | Stewart Butler | 15 | | Dunstable | 4:28.99 |
| 8 | 7 | Ethan Wallis | 15 | | Norwich Swan | 4:30.88 |
| Heat Number - 3 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 16 | Roan Brennan | 19 | S10 | Basildon Ph | 4:24.90 |
| 2 | 18 | Oliver Fuller | 15 | | Co Cambridge | 4:23.61 |
| 3 | 20 | Archie Tebbutt | 15 | | New Hall | 4:22.64 |
| 4 | 22 | Thomas Ford | 19 | | Basildon Ph | 4:21.90 |
| 5 | 21 | Thomas Spelman | 18 | | Stowmarket | 4:22.10 |
| 6 | 19 | Danylo Kravchenko | 16 | | New Hall | 4:23.01 |
| 7 | 17 | Patryk Nowak | 15 | | Co Peterboro | 4:24.17 |
| 8 | 15 | Luke Owens | 15 | | Putteridge | 4:24.93 |
| Heat Number - 4 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 24 | Oliver Fenwick | 16 | | Hatfield | 4:21.08 |
| 2 | 26 | Ben Davison | 20 | | Hatfield | 4:19.48 |
| 3 | 28 | Jake Lloyd | 30 | | Bishop Stort | 4:19.14 |
| 4 | 30 | Ben Howlett | 18 | | teamipswich | 4:18.75 |
| 5 | 29 | Will Riley | 16 | | teamipswich | 4:18.98 |
| 6 | 27 | George Carter | 17 | | Co Cambridge | 4:19.30 |
| 7 | 25 | K-Ets Yah-Khai | 16 | | Hatfield | 4:20.96 |
| 8 | 23 | Daniel Williams | 17 | | Hatfield | 4:21.29 |
| Heat Number - 5 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 32 | Zak Fellows | 16 | | Co St Albans | 4:18.50 |
| 2 | 34 | Jacob Bacon | 15 | | Co Peterboro | 4:16.15 |
| 3 | 36 | Kian Lee | 17 | | Co Peterboro | 4:14.96 |
| 4 | 38 | George Hooper | 18 | | Co St Albans | 4:11.61 |
| 5 | 37 | Conor Mint | 16 | | Basildon Ph | 4:12.02 |
| 6 | 35 | Oscar Hunter | 16 | | Norwich Swan | 4:15.65 |
| 7 | 33 | Daniel Thompson | 18 | | Thurrock | 4:17.40 |
| 8 | 31 | B Macdonald-Williams | 17 | | Bishop Stort | 4:18.65 |
| Heat Number - 6 |
| Lane | Comp.No. | Name | AaD | Cat | Club | Time |
| 1 | 40 | Harrison Shaw | 18 | | Flitwick | 4:10.40 |
| 2 | 42 | Robert Fenner | 17 | | Basildon Ph | 4:09.33 |
| 3 | 44 | Daniel McGuinness | 19 | | Basildon Ph | 4:07.70 |
| 4 | 46 | Daniel Belsey | 17 | | Hatfield | 4:01.08 |
| 5 | 45 | Ryan Wall | 18 | | Co Cambridge | 4:03.90 |
| 6 | 43 | Patch Robinson | 18 | | teamipswich | 4:07.80 |
| 7 | 41 | Adam O'Neal | 17 | | Bedford SS | 4:10.02 |
| 8 | 39 | Luke Martell | 19 | | Watford SC | 4:11.15 |