EVENT 507 Girls 12 Yrs/Over 800m Freestyle - Heats
| Heat Number - 1 |
| Lane | Comp.No. | Name | AaD | Club/Country | Time |
| 3 | 1 | Annabelle Brown | 12 | Stevenage | 12:01.81 |
| 4 | 3 | Abbie Hackworth | 12 | Hatfield | 11:49.90 |
| 5 | 2 | Aine Dunwoodie | 12 | Co St Albans | 11:57.21 |
| Heat Number - 2 |
| Lane | Comp.No. | Name | AaD | Club/Country | Time |
| 1 | 4 | Amy Harper | 12 | Watford SC | 11:47.08 |
| 2 | 6 | Raissa Vickery | 12 | Co St Albans | 11:34.71 |
| 3 | 8 | Niamh O'Meara | 13 | Watford SC | 10:54.44 |
| 4 | 10 | Heather Mann | 13 | Stevenage | 10:52.24 |
| 5 | 9 | Grace Cawley | 13 | Hemel Hemp | 10:53.94 |
| 6 | 7 | Megan Worley | 13 | Watford SC | 10:57.45 |
| 7 | 5 | Chloe Coster | 12 | Hatfield | 11:41.78 |
| Heat Number - 3 |
| Lane | Comp.No. | Name | AaD | Club/Country | Time |
| 1 | 12 | Charlotte Williams | 13 | Cheshunt | 10:39.76 |
| 2 | 14 | Gemma Nottage | 14 | Watford SC | 10:34.20 |
| 3 | 16 | Emilia Dunwoodie | 14 | Co St Albans | 10:32.94 |
| 4 | 18 | Katy Lane | 13 | Co St Albans | 10:20.74 |
| 5 | 17 | Caitlin O'Toole | 15 | Royston | 10:21.77 |
| 6 | 15 | Caitlin Hartley | 15 | Hatfield | 10:33.90 |
| 7 | 13 | Bella Parkus | 14 | Hoddesdon | 10:34.41 |
| 8 | 11 | Jessica Warne | 14 | Watford SC | 10:48.57 |
| Heat Number - 4 |
| Lane | Comp.No. | Name | AaD | Club/Country | Time |
| 1 | 20 | Sofia Peccei | 14 | Watford SC | 10:16.67 |
| 2 | 22 | Eleanor Mason | 16 | Bishop Stort | 10:12.44 |
| 3 | 24 | Alice Richardson | 16 | Co St Albans | 10:08.64 |
| 4 | 26 | Antonia Jubb | 14 | Hatfield | 10:06.55 |
| 5 | 25 | Eleanor Craig | 15 | Watford SC | 10:07.02 |
| 6 | 23 | Isabel Murtagh | 13 | Hatfield | 10:10.92 |
| 7 | 21 | Kiera Beaver | 15 | Watford SC | 10:14.33 |
| 8 | 19 | Georgia Pritchard | 14 | Hatfield | 10:17.34 |
| Heat Number - 5 |
| Lane | Comp.No. | Name | AaD | Club/Country | Time |
| 1 | 28 | Anastasia Wilkinson | 14 | Hatfield | 9:56.01 |
| 2 | 30 | Jessica Keogh | 15 | Hatfield | 9:53.69 |
| 3 | 32 | Jo Mitchinson | 40 | Stevenage | 9:43.46 |
| 4 | 34 | Lily Merrett | 16 | Co St Albans | 9:03.76 |
| 5 | 33 | Erin O'Meara | 16 | Watford SC | 9:18.15 |
| 6 | 31 | Lucy Park | 23 | Watford SC | 9:45.04 |
| 7 | 29 | Francesca Peccei | 16 | Watford SC | 9:55.58 |
| 8 | 27 | Ellie Holliss | 15 | Co St Albans | 10:01.10 |