| One Stop Maintain and Clean Ltd | Administrative & support | 2025 |
| One Stop Party Shop Mansfield Ltd | Wholesale & retail | 2024 |
| One Team Security Services Limited LP | | 2023 |
| One TUP Limited | Hospitality | 2023 |
| Onedrope Limited | Transport & logistics | 2025 |
| Onesite Solutions Limited | Manufacturing | 2003 |
| Onesoon Limited | Information & communication | 2003 |
| Onkar Properties Ltd | Real estate | 2016 |
| Online Waste Services Ltd | Water & waste | 2018 |
| OP3N24 Ltd | Transport & logistics | 2025 |
| OPA! Greek Ltd | Hospitality | 2023 |
| Openeyedexecutiveservices Ltd | Administrative & support | 2023 |
| OPT Property Ltd | Households | 2025 |
| Opti-Cut Automation Ltd | Manufacturing | 2018 |
| Optilight Electrical Services Limited | Construction | 2015 |
| Optima (Midlands) Ltd | Construction | 2023 |
| Optima Professional Cleaning Services Ltd | Water & waste | 2026 |
| Optimise Learning Ltd | Professional & scientific | 2022 |
| Options Keyworth Ltd | Wholesale & retail | 2019 |
| OQ Short Ltd | Transport & logistics | 2022 |
| Orbis Properties Limited | Real estate | 2018 |
| Orchard (Clinics 1) Limited | Construction | 2003 |
| Orchard (Clinics 2) Limited | Real estate | 2012 |
| Orchard (Clinics 3) Limited | Real estate | 2012 |
| Orchard (Clinics 4) Limited | Construction | 2003 |
| Orchard (Clinics 5) Limited | Construction | 2003 |
| Orchard (Clinics 6) Limited | Construction | 2003 |
| Orchard (Developments) Holdings Limited | Construction | 1991 |
| Orchard (Huthwaite) Limited | Extraterritorial | 2002 |
| Orchard Developments Limited | Administrative & support | 1990 |
| Orchard Executive Homes Limited | Construction | 1996 |
| Organic Packages Limited | Transport & logistics | 2022 |
| Orico Limited | Wholesale & retail | 2026 |
| Oriental Forest Ltd | Hospitality | 2025 |
| Orin Business Ltd | Wholesale & retail | 2026 |
| Orwin House RTM Company Limited | Households | 2016 |
| Oscar Bulding Ltd | Construction | 2025 |
| Oskar Market Ltd | Wholesale & retail | 2025 |
| Ostranch Ltd | Wholesale & retail | 2025 |
| Ostranch Properties Ltd | Real estate | 2025 |
| OT Food Limited | Hospitality | 2025 |
| OTB Recovery & Transport Ltd | Transport & logistics | 2025 |
| OTHERTHINGS2020 Ltd | Wholesale & retail | 2019 |
| OTN Property Ltd | Real estate | 2025 |
| Otto Limited | Construction | 2001 |
| OUGHT2 Ltd | Professional & scientific | 2020 |
| OUR Sound Music Ltd | Arts & recreation | 2021 |
| Outdoor Design 4U Limited | Administrative & support | 2018 |
| Outdoor Design Consultancy Ltd | Professional & scientific | 2023 |
| Outlet Ltd | Wholesale & retail | 2026 |
| Outside the Cave C.I.C. | Other services | 2017 |
| Ouvero Limited | Wholesale & retail | 2025 |
| Overton Electrical Services Ltd | Construction | 1998 |
| Overton Fire & Security Ltd | Construction | 2025 |
| Overton Installations Ltd | Construction | 2020 |
| OX Singh Ltd | Administrative & support | 2022 |
| Oxatim Ltd | Wholesale & retail | 2023 |
| Oxclose Food Market Limited | Wholesale & retail | 2006 |
| Oxford Road (Market Rasen) Ltd | Households | 2018 |
| Oxford Street Carpets Ltd | Wholesale & retail | 2022 |
| Oxton Hill Alpacas Ltd | Agriculture & fishing | 2026 |
| OZ Leisure Limited | Wholesale & retail | 2014 |
| OZ Pizza Ltd | Hospitality | 2026 |
| OZ Read Ltd | Administrative & support | 2022 |
| O’Meara-Group Ltd | Real estate | 2025 |
| P & D Properties (Midlands) Limited | Real estate | 2005 |
| P & P Accomodations Ltd | Real estate | 2021 |
| P & P Merchandising Limited | Administrative & support | 2000 |
| P & R Automotives Limited | Wholesale & retail | 2024 |
| P & S Brands LLP | | 2018 |
| P B Waste Ltd | Mining & quarrying | 2006 |
| P Burtt Limited | Real estate | 2020 |
| P Harrison (UK) Ltd | Construction | 2016 |
| P J Uptime Limited | Information & communication | 2020 |
| P W Earthing Consultancy Ltd | Administrative & support | 2022 |
| P&G Catering Ltd | Hospitality | 2026 |
| P&P Convenience Stores Ltd | Wholesale & retail | 2017 |
| P&P London Properties Ltd | Real estate | 2018 |
| P&P Stores Ltd | Other services | 2024 |
| P&S Haulage Limited | Transport & logistics | 2018 |
| P&S Telnet UK Ltd | Construction | 2024 |
| P. Atkins (Fuel Injection) Limited | Wholesale & retail | 1976 |
| P. J. Barsby Plumbing & Heating Limited | Construction | 2009 |
| P. Stanley Builders Limited | Construction | 2011 |
| P.C.S. (Mansfield) Limited | Real estate | 2003 |
| PA Products Ltd | Wholesale & retail | 2020 |
| Pacher Ltd | Professional & scientific | 2014 |
| Pacs (Mansfield) Ltd | Professional & scientific | 2024 |
| PAD & Nessa Properties Ltd | Construction | 2023 |
| Padda Investment Properties Ltd | Real estate | 2018 |
| Padda Retail Limited | Wholesale & retail | 2008 |
| Padiham Ltd | Administrative & support | 2022 |
| Padlupp Ltd | Information & communication | 2025 |
| Paint and Decks Ltd | Construction | 2023 |
| Paint Chip Techniques Limited | Wholesale & retail | 1997 |
| Painted Hall Ltd | Real estate | 2017 |
| Paling Administration Ltd | Administrative & support | 2025 |
| Pallant Developments Limited | Construction | 2023 |
| Pamper Life Travel Limited | Administrative & support | 2018 |
| Panandpaper Limited | Hospitality | 2022 |