| Irish Peat Development Company Limited | Co.Antrim | 1902 |
| Irish Seed Potatoes Limited | | 1981 |
| Irish Wagyu Ltd | Newry | 2014 |
| Irish Wolfhound UK Northamptonshire Ltd | Corby | 2026 |
| Irishcombe Farms Limited | South Molton | 2026 |
| IRM Enterprises Limited | Eastbourne | 2005 |
| Irnham Estate | Nr Grantham | 1936 |
| Ironbush Dairy Farm Limited | Melton Mowbray | 2019 |
| Ironside Marine Ltd | Fraserburgh | 2025 |
| Ironstride Farriery Solutions Ltd | Loughborough | 2025 |
| Ironwater Group Ltd | Gainsborough | 2026 |
| Ironwood Stables Ltd | Wallington | 2025 |
| Irresista-Bulls UK Limited | Hull | 2020 |
| Irvine Hoof Trimming Ltd | Castlewellan | 2018 |
| Irving Agronomy Limited | Stafford | 2025 |
| Irwell View Farm Limited | Bury | 2025 |
| Irwin Farming Limited | Nottingham Business Park | 2003 |
| Irwin Leasing Ltd | Diss | 2004 |
| IS Agri UK Ltd | Liverpool | 2025 |
| Isaac Bargh Hoof Trimming Limited | Kendal | 2017 |
| Isaac Benson Limited | Kendal | 2008 |
| Isadale Limited | Thornton-Cleveleys | 2016 |
| Isadale Marine Services Ltd | Thornton-Cleveleys | 2019 |
| Isah Sustainable Farming Ltd | Farnborough | 2022 |
| Isambard Limited | Sandy | 2014 |
| ISC Tree Specialist Limited | Cranbrook | 2004 |
| Iscoed Farms Limited | Dyfed | 2003 |
| Isencea Limited | Kington | 2019 |
| Isherwood & Company Ltd | Chulmleigh | 2014 |
| Ishga Ltd | Stornoway | 2015 |
| Isis Forestry Limited | Market Harborough | 2010 |
| Islamara Limited | Turriff | 2022 |
| Island ARB and Groundworks Ltd | Colchester | 2014 |
| Island Community Haven CIC | Nottingham | 2020 |
| Island Dairies Farm Limited | Dromore | 2021 |
| Island Farms NI Limited | Magherafelt | 2010 |
| Island Fish Limited | Isles Of Scilly | 2015 |
| Island Hemp Farm Limited | Liverpool | 2018 |
| Island Highland Limited | Sheerness | 2025 |
| Island Honey Limited | Leyland | 2026 |
| Island Lake France Limited | Ashford | 2019 |
| Island Marine Systems Limited | Shetland | 2003 |
| Island Pest Control Limited | Ryde | 2005 |
| Island Pigs Ltd | Colchester | 2012 |
| Island Tiger Limited | Isles Of Scilly | 2007 |
| Island Tree Services Ltd | Ventnor | 2026 |
| Islandderry Trout Fishery Limited | Dromore | 2024 |
| Islander Direct Shellfish Limited | Oban | 2023 |
| Islander Kelp Ltd | Ballycastle | 2013 |
| Islay Development Initiative Ltd | Isle Of Islay | 2003 |
| Islay Estates Company | Salisbury | 1928 |
| Isle Fruits (Somerset) Limited | Taunton | 2023 |
| Isle Fruits Limited | Taunton | 2023 |
| Isle Grow Greens Limited | Freshwater | 2019 |
| Isle of Barra Oysters Ltd | Glasgow | 2013 |
| Isle of Barra Shellfish Limited | Dunoon | 2025 |
| Isle of Berneray Seafoods Ltd | Isle Of North Uist | 2026 |
| Isle of Canty Kennels Limited | Dunfermline | 2019 |
| Isle of ELY KOI Ltd | Downham Market | 2002 |
| Isle of Mull Oysters Limited | Golspie | 2004 |
| Isle of Skye Mussel Company Limited | Tarskavaig | 2004 |
| Isle of Skye Salmon Limited | Stirling | 2019 |
| Isle of Skye Shellfish Ltd | Isle Of Skye | 2021 |
| Isle of Wight Mushrooms Limited | Ryde | 2019 |
| Isle Provenance Honey Limited | Waterlooville | 2021 |
| Isle Ride to Recover CIC | Belton | 2025 |
| Isleham Carrot Growers Limited | Ely | 1990 |
| Islerose Limited | Biggar | 1995 |
| Isles of Scilly Nature Co. Ltd | London | 2024 |
| Ismn Limited | Chatham | 2018 |
| Isolde Farms Ltd | Peterborough | 1997 |
| Israel Haifa PUS Liquid Industry Group Limited | Milton Keynes | 2025 |
| Issec Limited | Salisbury | 2002 |
| It's the Leash WE CAN DO Ltd | Widnes | 2024 |
| It.Com Ltd. | Edinburgh | 1998 |
| Itchenor Gate Farms | West Sussex | 1962 |
| Itchigoitchi Ltd | Nottingham | 2024 |
| Itec Components Limited | West Yorkshire | 2001 |
| Itenio Limited | Newbury | 2015 |
| Ithon Valley Farmers Group Ltd | Llandrindod Wells | 2026 |
| ITM Engineering Limited | Inverness | 2015 |
| Itsinc Ltd | Banbury | 2018 |
| Itty Bitty Kitty Tails Ltd | Blackburn | 2021 |
| Iucn Coin Ltd | Hertfordshire | 2022 |
| IV Tree Services Ltd | Inverness | 2024 |
| IVA Tucker One Trading Limited | Liverpool | 2015 |
| IVA Tucker Three Trading Limited | Liverpool | 2015 |
| Ivan Ambrose and Company Limited | Lydiate | 1957 |
| Ivan Mcalister Ltd | Caledon | 2016 |
| Ivan Megaw & SON Limited | Craigavon | 2019 |
| Ivan Slater Limited | Preston | 2002 |
| Ivan Toms Limited | Ivybridge | 2015 |
| Ivanda Nursery Limited | Spalding | 2005 |
| Ivor Duggan & Sons Limited | Hereford | 1987 |
| Ivor Gaston & SON Ltd | Duns | 2012 |
| Ivory (Eco) Ltd | Derby | 2021 |
| IVY & Friends Limited | Peterborough | 2025 |
| IVY Equestrian Limited | Cardiff | 2025 |
| IVY Farm (Coddenham) Limited | Norwich | 1982 |
| IVY Farm Christmas Trees and Events Limited | North Walsham | 2025 |