| Olive Locum Ltd | Health & social care | 2025 |
| Olive Tree Grove Limited | Real estate | 2025 |
| Oliver's Barber Shop Ltd | Other services | 2019 |
| Olivia Grace Interiors Limited | Construction | 2018 |
| Olympus Electrical Services Ltd | Manufacturing | 2018 |
| Olympus Holdings (Lincs) Ltd | Financial services | 2026 |
| Olympus Property (Lincs) Ltd | Real estate | 2026 |
| OM Consultants Ltd | Professional & scientific | 2011 |
| OM SAI Store Ltd | Wholesale & retail | 2017 |
| Omega Haulage Limited | Transport & logistics | 2003 |
| Omega UK Limited | Transport & logistics | 2003 |
| Omerta (GB) Ltd | Real estate | 2004 |
| Omni Health Limited | Health & social care | 2024 |
| Omniscientai Ltd | Information & communication | 2026 |
| Omoyine Limited | Real estate | 2025 |
| ON the DOT VA Ltd | Information & communication | 2025 |
| One CAP Electrical Services Ltd | Construction | 2021 |
| One Connectivity Limited | Information & communication | 2013 |
| One Eighteen Limited | Wholesale & retail | 2016 |
| One Point Renewables Limited | Administrative & support | 2022 |
| One Stop Musculoskeletal Ltd | Health & social care | 2015 |
| One Stop Shop (Lincs) Limited | Wholesale & retail | 2013 |
| One Way UK Limited | Arts & recreation | 2003 |
| One-Africa Proent UK Ltd | Information & communication | 2025 |
| Online Fulfilment Centre Limited | Wholesale & retail | 2006 |
| Online Motor Group Ltd | Wholesale & retail | 2015 |
| Online Tilesuk Limited | Wholesale & retail | 2013 |
| Online Web Studio Ltd | Information & communication | 2023 |
| Only Fools and Fences Ltd | Construction | 2026 |
| Onlyvibes Ltd | Professional & scientific | 2026 |
| Onyx Investco Limited | Real estate | 2023 |
| Onyx Medico Limited | Professional & scientific | 2012 |
| Onyx Property Solutions Ltd | Real estate | 2017 |
| Open Door Care C.I.C | Health & social care | 2007 |
| Openhaus Limited | Real estate | 2018 |
| Optima Plus Medics Ltd | Health & social care | 2023 |
| Optimal Educational (Grimsby) Limited | Education | 2006 |
| Optimia Ltd | Information & communication | 2016 |
| Optis Europe Limited | Administrative & support | 2000 |
| Optus Group Limited | Administrative & support | 2025 |
| Opulent Bathrooms and Tiles Ltd | Professional & scientific | 2026 |
| Opus Business Management Ltd | Professional & scientific | 2023 |
| Oranda Engineering Limited | Professional & scientific | 2024 |
| Orca Industrial Services Limited | Construction | 2025 |
| Orchard (Stamford) Limited | Construction | 2010 |
| Orchard Developments 21 Limited | Construction | 2021 |
| Orchard Properties Lincolnshire Ltd | Construction | 2012 |
| Orchid Homes Management Company Limited | Real estate | 2008 |
| Ordix Limited | Health & social care | 2023 |
| Origin Electrical Services Ltd | Construction | 2020 |
| Origom Properties Ltd | Construction | 2025 |
| Origom Services Limited | Construction | 2024 |
| Origom UK Holdings Ltd | Financial services | 2023 |
| Orix Retails Limited | Wholesale & retail | 2019 |
| Orlams Limited | Health & social care | 2021 |
| Osborne Financial Limited | Professional & scientific | 2023 |
| Osborne Insulations Ltd | Other services | 2025 |
| Osborne’S Plumbing Ltd | Construction | 2024 |
| Oscar Cleve Limited | Wholesale & retail | 2002 |
| Oscars (Grimsby) Limited | Wholesale & retail | 1995 |
| Oskiera Transport Ltd | Transport & logistics | 2020 |
| OSL Fleet Services Ltd | Other services | 2019 |
| Osmaro Trans Ltd | Transport & logistics | 2017 |
| Osprey 54 Ltd | Professional & scientific | 2019 |
| Osprey Fish Trading Limited | Wholesale & retail | 2023 |
| Ostara East CIC | Other services | 2025 |
| Othello Restaurant GY Limited | Hospitality | 2013 |
| OUR Avenue Developments Limited | Construction | 2024 |
| OUR Big Picture Limited | Arts & recreation | 2016 |
| OUR Tots Tribe Ltd | Health & social care | 2018 |
| Ourcar Ltd | Wholesale & retail | 2021 |
| Outcomes of Care Ltd | Professional & scientific | 2010 |
| Outdoor Kitchens MCR Ltd | Manufacturing | 2022 |
| Outdoor Learning Consultancy Ltd | Education | 2013 |
| Outdoor Learning Schools C.I.C. | Hospitality | 2014 |
| Ovennchillers Ltd | Manufacturing | 2026 |
| Overcc Limited | Construction | 2026 |
| Overscope Limited | Construction | 2003 |
| Ovidiu Trans SRL Limited | Transport & logistics | 2025 |
| Ovilogistics Ltd | Transport & logistics | 2020 |
| Ovsrl Limited | Transport & logistics | 2025 |
| Owcam Automotive Limited | Wholesale & retail | 2018 |
| Owilson Properties Limited | Real estate | 2025 |
| Oxford Street Motors Ltd | Wholesale & retail | 2020 |
| Oyster Court Management Company Limited | Real estate | 2001 |
| Ozoned Limited | Real estate | 2015 |
| OZPOM25 Ltd | Hospitality | 2025 |
| P & a Barton Limited | Transport & logistics | 2005 |
| P & a C Whitfield Driver Solutions Limited | Transport & logistics | 2007 |
| P & K Property (Humberston) Ltd | Real estate | 2020 |
| P & L Discount Furniture Limited | Wholesale & retail | 2008 |
| P and T Energy Solutions Ltd | Administrative & support | 2015 |
| P B Garden & House Services Limited | Other services | 2003 |
| P B Residential Care Limited | Health & social care | 2000 |
| P B S Scaffolding Services ( Lincs. ) Ltd | Construction | 2025 |
| P D H Developments Limited | Professional & scientific | 1959 |
| P D M Property Limited | Households | 2016 |
| P G D Limited | Wholesale & retail | 2012 |
| P Myers Limited | Construction | 2006 |
| P Reynard Ltd | Manufacturing | 2016 |