| Orkney Farms Limited | Orkney | 2020 |
| Orkney Goose Hunts Ltd | Preston | 2020 |
| Orkney Green Ltd | Orkney | 2022 |
| Orkney Oysters Ltd | Stromness | 2019 |
| Orkney Scallops Ltd | Kirkwall | 2019 |
| Orkney Sea Farms Limited | Stirling | 1989 |
| Orkney Shellfish Hatchery Limited | Aultbea | 2017 |
| Orkney Shellfish Limited | Orkney | 1992 |
| Orlandos PVT Ltd | Rochdale | 2019 |
| Orleigh Farms Limited | Bideford | 1954 |
| Orlock Limited | Ballynahinch | 1987 |
| Orman (Carrolls Farm) Limited | Norfolk | 1958 |
| Orme Trading Ltd | Norwich | 2025 |
| Ormitton Limited | London | 2023 |
| Ormsary Scallops Limited | Port Glasgow | 1976 |
| Ornex Vantis Group Ltd | London | 2026 |
| ORR Developments Limited | Scarborough | 2012 |
| ORR Foodie Limited | Cupar | 2016 |
| Orrdone Farms Limited | Carlisle | 2015 |
| Orsett Estates Limited | Grays | 2008 |
| Orsett Park Farm Limited | London | 2019 |
| Orsfield Limited | Rotherham | 2025 |
| Orswell Farm Ltd | Chelmsford, Essex | 2019 |
| Ortir Ltd | Cardigan | 2021 |
| Orton House Farm Dairy Limited | Atherstone | 2026 |
| Orton House Farm Poultry Limited | Atherstone | 2026 |
| Orwell Marine Limited | Felixstowe | 2020 |
| OS Agri and Fencing Limited | Horsham | 2025 |
| OS Utility Project Ltd | Billericay | 2025 |
| OSA Vivere Ltd | Glasgow | 2022 |
| Osado Farm Management Limited | Perth | 2010 |
| Osberton Mill Farm Ltd | Worksop | 2022 |
| Osberton Stud Limited | Retford | 2002 |
| Osborn Equine Limited | Taunton | 2019 |
| Osborne Agri Company Private Limited | London | 2023 |
| Osborne Farm Holdings Ltd | Beech Hill | 2019 |
| Osborne Farming Ltd | Taunton | 2012 |
| Osborne Tree Services Ltd | Castle Cary | 2022 |
| Oscar & Co Meadows Ltd | Southampton | 2026 |
| Oscar Crocker Ltd | Reading | 2024 |
| Osgerby & Chantrey Limited | Hull | 2002 |
| Osgodby Farm Ltd | Peterborough | 2023 |
| OSH Dressage Ltd | Colchester | 2018 |
| Osmaston Farrant Agricultural Services Ltd | Billingshurst | 2026 |
| Osmonds Timber Limited | Uckfield | 2016 |
| Osny Link Co., Ltd | Cambridge | 2025 |
| Osprey (Jacoba Maria) Ltd | Aberdeen | 2017 |
| Osprey (PD147) Limited | Aberdeen | 1998 |
| Osprey (PD156) Limited | Aberdeen | 1998 |
| Osprey (PD357) Limited | Aberdeen | 1998 |
| Osprey (PD43) Limited | Aberdeen | 1998 |
| Osprey (PD63) Limited | Aberdeen | 1998 |
| Osprey (PW447) Limited | Aberdeen | 2002 |
| Osprey AH35 Ltd. | Arbroath | 2010 |
| Osprey Farms Limited | Meigle | 2024 |
| Osprey II Ltd | Fraserburgh | 2020 |
| Osprey Vessel Management Limited | Peterhead | 2010 |
| Oss-I-Chaff Limited | Nottinghamshire | 1996 |
| Ossbey Ltd | London | 2023 |
| Osse Forestry Limited | Abingdon | 2022 |
| Ossquoy Limited | Orkney | 2005 |
| Osterley Park Farm Limited | Middlesex | 1957 |
| Ostlers Nurseries Limited | Nantwich | 2003 |
| Ostridge Contractors Ltd | Robertsbridge | 2017 |
| Oswald Potter Farms (Kirklington) Limited | Thirsk | 1977 |
| Oswest Limited | Chester | 2017 |
| Oswestry and District Agricultural Society | Oswestry | 1999 |
| Oswestry Equestrian Limited | Oswestry | 2021 |
| Oswestry Livestock Auctions Limited | Oswestry | 2012 |
| OT Breeding Limited | Newmarket | 2023 |
| Othniel Oysters Limited | Dorset | 2006 |
| Othniel Shellfish Limited | Dorset | 1993 |
| Otium Farm Ltd | Ashford | 2026 |
| Otley Cattle Market Auction Limited | Otley | 1932 |
| Otter Arable Limited | Northumberland | 1998 |
| Otter Ferry Land and Sea Limited | Argyll | 1977 |
| Otter Ferry Seafish Limited | Argyll | 1992 |
| Otter Initiatives Ltd | Llandysul | 2024 |
| Otterlee Farm Ltd | Sowerby Bridge | 2018 |
| Otters Holt Haylage Co Ltd | Haverfordwest | 2013 |
| Ottershaw Tree Services Ltd | Addlestone | 2018 |
| Otterwood Cottage Ltd | Spilsby | 2025 |
| Otter’S Holt Farm Ltd | London | 2024 |
| Ottevanger Milling Engineers Limited | Reigate | 2021 |
| Otto's Family Farm Ltd | Chelmsford | 2026 |
| Ottogi Limited | Aberdeen | 2025 |
| Ottoman & Sons Ltd | Birmingham | 2025 |
| Ouchim Songdi (UK) Biochemical Co., Ltd | West Midlands, England | 2025 |
| Oulton Farming Limited | Stoke-On-Trent | 2025 |
| Oulton House Farm Limited | Stafford | 2008 |
| Oulton Lowe Farms Limited | Macclesfield | 2019 |
| Oulton View Farm Ltd | Tarporley | 2009 |
| OUR Back Yard Ltd | Warrington | 2021 |
| OUR Big Shop Ltd | London | 2025 |
| OUR Boy’S Bees Ltd | Cheltenham | 2023 |
| OUR Environmental Department Limited | Dulverton | 2007 |
| OUR Food Trust | Crickhowell | 2017 |
| OUR JIM (SW) Limited | Cheltenham | 2025 |
| OUR Lass Limited | Ruswarp | 2020 |
| OUR Little Home Farm Limited | Cleckheaton | 2025 |