| Oppisec Ltd | Professional & scientific | 2024 |
| Opsapp Global Limited | Administrative & support | 2025 |
| Opti-U Ltd | Information & communication | 2025 |
| Optima Claims Ltd | Administrative & support | 2020 |
| Optima Graphic Design Consultants Limited | Administrative & support | 2000 |
| Optimal Biogas Ltd | Energy | 2018 |
| Optimal Design Limited | Construction | 2017 |
| Optimum Global Care Ltd | Health & social care | 2023 |
| Optimum Health Supplements Ltd | Wholesale & retail | 2012 |
| Optimum Safety Ltd | Health & social care | 2017 |
| Option 3 Pizza Ltd | Hospitality | 2026 |
| Option Green Ltd | Other services | 2024 |
| Option Lincoln Ltd | Hospitality | 2017 |
| Optique Vision (Lincoln) Limited | Wholesale & retail | 2013 |
| Optysio Ltd | Other services | 2024 |
| Orak Ltd | Hospitality | 2019 |
| Orange Health Limited | Health & social care | 2016 |
| Orange Holdings Limited | Real estate | 2020 |
| Orbis Tourism Consultancy Ltd | Professional & scientific | 2025 |
| Orby Pubs Inns Limited | Hospitality | 2017 |
| Orchard Close Management Company (Newton-On-Trent) Limited | Administrative & support | 2006 |
| Orchard Flaxen Ltd | Professional & scientific | 2023 |
| Orchard Funeral Services Limited | Other services | 2016 |
| Orchard Garth Management Limited | Households | 1997 |
| Orchard Leisure Park Limited | Hospitality | 2009 |
| Orchard Park (Lincoln) Limited | Households | 2004 |
| Orcycle Ltd | Health & social care | 2026 |
| Organic Solutions Consulting LLP | | 2018 |
| Organic Solutions Property Ltd | Other services | 2015 |
| Organised Sport & Event Travel Ltd | Administrative & support | 2007 |
| Oriel Publishing Ltd | Information & communication | 2025 |
| Orient 66 Limited | Hospitality | 2020 |
| Orient Chinese Food Limited | Hospitality | 2026 |
| Oriental City (2018) Limited | Hospitality | 2018 |
| Origami Orange Limited | Other services | 2010 |
| Origin Chips Consultancy Limited | Professional & scientific | 2025 |
| Origin Design Studio Limited | Professional & scientific | 2011 |
| Original Parts Supply Ltd | Wholesale & retail | 2019 |
| Originals by Grace Munro Ltd | Arts & recreation | 2021 |
| Orisel Limited | Administrative & support | 2015 |
| Ormz Limited | Wholesale & retail | 2025 |
| Orsted Recruitment Limited | Administrative & support | 2017 |
| Orthojoint Services Ltd | Health & social care | 2013 |
| Orthopod Medical Services Ltd | Health & social care | 2020 |
| OS Sport Massage Ltd | Health & social care | 2025 |
| Osbourne Blinds & Interiors Ltd | Wholesale & retail | 2016 |
| Osiris Educational Woodhall Spa Limited | Education | 2005 |
| Otars Transport Ltd | Transport & logistics | 2018 |
| Otis & Ridley Ltd | Real estate | 2022 |
| Otis Cleary Racing Limited | Arts & recreation | 2025 |
| OTM Engineering Limited | Professional & scientific | 2006 |
| Otter Builders Limited | Construction | 2014 |
| Otter Candle Co Ltd | Wholesale & retail | 2018 |
| Otter Homes (Lincoln) Ltd | Construction | 1971 |
| OTV Holdings Ltd | Financial services | 2025 |
| OUR Elderly Care Ltd | Health & social care | 2025 |
| Ourons Ltd | Wholesale & retail | 2017 |
| OUT of the Box Counselling Ltd | Health & social care | 2024 |
| Outasight (Shower Screen) Ltd | Manufacturing | 2013 |
| Outasight Shower Screen (UK) Ltd | Manufacturing | 2020 |
| Outdoor Events (Lincoln) Limited | Hospitality | 2025 |
| Oval News Retail Ltd | Wholesale & retail | 2022 |
| Over the Edge Access Solutions Ltd | Construction | 2025 |
| Overfield Park Limited | Extraterritorial | 2019 |
| Overland Transport & Trading Company Limited(The) | Transport & logistics | 1964 |
| Overland Travels Ltd | Transport & logistics | 2024 |
| Owen Heath Ltd | Health & social care | 2025 |
| Owen-Johnstone Ltd | Health & social care | 2012 |
| OX Ltd | Wholesale & retail | 2018 |
| OX Products Group UK Limited | Wholesale & retail | 2011 |
| OX Products UK Limited | Extraterritorial | 2011 |
| OX Tools Global Holdings Ltd | Financial services | 2022 |
| OX Tools Global Investments Limited | Financial services | 2022 |
| OX Tools Ltd | Extraterritorial | 2015 |
| OX Tools Shared Services Limited | Administrative & support | 2011 |
| OX Tools UK Ltd | Extraterritorial | 2015 |
| Oxflow Limited | Wholesale & retail | 2007 |
| Oxford & Lincoln Ltd | Real estate | 2022 |
| Oxford Health Associates LLP | | 2026 |
| Oxford Urology Associates LLP | | 2016 |
| Oziox Medical Consultancy Limited | Health & social care | 2023 |
| Ozkasap Meal Ltd | Hospitality | 2026 |
| P & a Properties (Lincs) Limited | Real estate | 2025 |
| P & L Haulage Ltd | Transport & logistics | 2026 |
| P & L Service and Maintenance Ltd | Wholesale & retail | 2025 |
| P & S Simpson Limited | Transport & logistics | 2007 |
| P a Arden & SON Holdings Limited | Construction | 2023 |
| P a Arden & SON Limited | Construction | 2014 |
| P a Gibbons Limited | Construction | 2006 |
| P a Tyson Consulting Ltd | Professional & scientific | 2025 |
| P J F Landscapes Limited | Administrative & support | 2007 |
| P J Mcgann Electrical Ltd | Construction | 2025 |
| P P Goodall Urology Ltd | Health & social care | 2020 |
| P P H Construction Ltd | Administrative & support | 2014 |
| P Young Electrical Services Limited | Construction | 2011 |
| P&C Estates Holdings Ltd | Real estate | 2021 |
| P&G Hood Consulting Ltd | Professional & scientific | 2014 |
| P&J Sons Ltd | Wholesale & retail | 2025 |
| P&K Developments Limited | Real estate | 2025 |
| P&L Property Ventures Ltd | Other services | 2022 |