| Nymet Tracey Contractors Limited | Crediton | 2004 |
| Nysafawn Sporting Ltd | Newcastle Upon Tyne | 2025 |
| O & a Agro Allied Ltd | Tilbury | 2020 |
| O & K Forestry Ltd | Ayr | 2025 |
| O & L East Livestock Ltd | Alresford | 2023 |
| O B H Fallen Stock Ltd | Cirencester | 2013 |
| O Bevan Contracting Limited | Eldwick | 2026 |
| O C H Investment Ltd. | Kington | 2014 |
| O Connor Arboriculture Limited | Matlock | 2025 |
| O D Roberts CYF | Porthmadog | 2018 |
| O Doogan Services Ltd | Shetland | 2025 |
| O E Hunt Ltd | Milngavie | 2024 |
| O Frost Forestry & Arboriculture Limited | Street | 2017 |
| O G Thomas Amaethyddiaeth CYF | Dyffryn Ardudwy | 2019 |
| O J Munday Farms Ltd | King'S Lynn | 2017 |
| O J Neil Biomass Limited | Bury St. Edmunds | 2016 |
| O J P Contracts Ltd | Hertford | 2017 |
| O J T Tree Services Ltd | Northwich | 2019 |
| O K Poultry Genetics Ltd | Preston | 2018 |
| O M Davies & Sons Limited | Cardigan | 2009 |
| O P Farming Ltd | Colwyn Bay | 2024 |
| O P Hoddinott and Sons Limited | Taunton | 2007 |
| O T Sparks Farming Ltd | Pontyclun | 2025 |
| O&J Contracting Limited | Macclesfield | 2019 |
| O&M Equestrian Ltd | Bristol | 2024 |
| O'Callaghan Tree Surgeons Limited | Wiltshire | 2002 |
| O'Donnell Farms Ltd | Dungannon | 2015 |
| O'Donnell Racing Limited | Barnsley | 2021 |
| O'Dwyer Consulting Services Limited | East Grinstead | 2024 |
| O'Gara Contracts Ltd | | 2002 |
| O'Hara Agricultural Limited | Quorn | 2021 |
| O'Hara Farms Ltd | Limavady | 2023 |
| O'Kane Family Farms Ltd | Omagh | 2015 |
| O'Kane Farms Limited | Ballymena | 2014 |
| O'Keefe Enterprises Limited | Newtownbutler | 2019 |
| O'Malley Acres Ltd | Belfast | 2024 |
| O'Malley Farms Ltd | Enniskillen | 2020 |
| O'Mara Fishing Ltd | Swansea | 2024 |
| O'Neill Smith Limited | Cowfold | 2004 |
| O'Neill Vegetables Ltd | Dungannon | 2023 |
| O'Pyzer Ltd | Taunton | 2024 |
| O'Reilly Agri Contracts Ltd | Armagh | 2024 |
| O'Sullivan & Edmonds Limited | Stoke-On-Trent | 2013 |
| O'Sullivan Farms Limited | Horsham | 1997 |
| O-Fish-Shell Limited | Lochgilphead | 1987 |
| O. Kinch Agricultural Contracting Ltd | Chandler'S Ford | 2017 |
| O. Palmer Limited | Brandon | 2019 |
| O.A. Taylor & Sons Farms Limited | Spalding | 2021 |
| O.A.Taylor & Sons Bulbs Limited | Holbeach Spalding | 1970 |
| O.B. Fishing Company Ltd. | Buckie | 2000 |
| O.C Woodley Agri Contractor Ltd | Slinfold | 2026 |
| O.C. Whittaker & Sons Limited | London | 1955 |
| O.C.Colston Limited | Oxon | 1957 |
| O.H.Footitt Agricultural & Property Ltd | Nottingham | 2024 |
| O.J.Roberts & Co Ltd | Ty Croes | 2013 |
| O.P. Shellfish Limited | Bridlington | 2013 |
| O.S. Agri Limited | Lowestoft | 2022 |
| O.T.E.C.Limited | Stockton-On-Tees | 1971 |
| O.W. Wortley & Sons Limited | Methwold Thetford | 1972 |
| O5 Farming Limited | Beverley | 2026 |
| OA Enterprises Ltd | London | 2026 |
| Oak & Finch Ltd | Coventry | 2025 |
| Oak & Willow Ltd | London | 2023 |
| Oak Barton Farm CIC | Peterborough | 2024 |
| Oak Cottage Enterprises Limited | Nottingham | 2003 |
| Oak Crest Ltd | London | 2022 |
| Oak Farm Livery Yard Limited | Ely | 2021 |
| Oak Farm Ltd | Henley On Thames | 2016 |
| Oak Forestry Ltd | Edinburgh | 2019 |
| Oak Haven Collective CIC | Edenbridge | 2024 |
| Oak Hill Farm Ltd | Dudley | 2023 |
| Oak House Farm Limited | Ipswich | 1991 |
| Oak LEA Farm Limited | Howes Lane Coventry | 2026 |
| Oak Meadow Limited | Worcester | 1988 |
| Oak Park Farm (Burgh Castle) Limited | Great Yarmouth | 2019 |
| Oak Park Farms Limited | Norwich | 1999 |
| Oak Tree Alpacas Limited | Nottingham | 2020 |
| Oak Tree Animals' Charity | Carlisle | 2016 |
| Oak Tree Beef Ltd | St. Albans | 2023 |
| Oak Tree Farm - Brixworth Ltd | Northampton | 2025 |
| Oak Tree Farm Limited | Haverfordwest | 1954 |
| Oak Tree Farm Rural Project Limited | Stone | 2010 |
| Oak Tree Land Management & Property Services Ltd | Blackburn | 2025 |
| Oak Tree Stables Ltd | Ruislip, | 2025 |
| Oak Vale Farms Ltd | Blandford | 2019 |
| Oak Vale Genetics Ltd | Spennymoor | 2023 |
| Oak Valley Tree Services Ltd | Okehampton | 2021 |
| Oak, ASH and Thorn Contracting Ltd | Sudbury | 2025 |
| Oakandyew Ltd | Sutton | 2020 |
| Oakapple Community Farm | Sheffield | 2020 |
| Oakapplefarm Ltd | Sheerness | 2013 |
| Oakbank Farm Holdings Ltd | East Calder | 2020 |
| Oakbank Game & Conservation Ltd | Ross-On-Wye | 2004 |
| Oakbrook Orchard Community Interest Company | Stroud | 2024 |
| Oakdale (NE) Limited | Saltburn By The Sea | 2008 |
| Oakdale Farm Cheshire Ltd | Sandbach | 2024 |
| Oakden Tree Care Ltd | Rye | 2025 |
| Oakenshaw Kennels Ltd | Wakefield | 2019 |
| Oakes Wildlife Management Ltd | Steventon | 2017 |
| Oakey Tree Services Ltd | Reading | 2021 |