| Nutrient Mitigation Limited | Professional & scientific | 2021 |
| Nutritionwise Limited | Health & social care | 2016 |
| NVO Limited | Administrative & support | 2003 |
| Nvsble Lasers Limited | Wholesale & retail | 2023 |
| Nvss Limited | Health & social care | 2024 |
| NW Consultancy Services Limited | Professional & scientific | 2016 |
| NXT GEN Electrical Ltd | Construction | 2022 |
| Nyoni PVT Ltd | Health & social care | 2014 |
| Nysander Lourenco Ltd | Hospitality | 2019 |
| O Swift Lettings Limited | Real estate | 2026 |
| O&K Ltd | Wholesale & retail | 2016 |
| O'Consultancy Ltd | Administrative & support | 2017 |
| O'Friends Holdings Limited | Financial services | 2024 |
| O'Mahoney Promotions Limited | Hospitality | 2026 |
| O'Nion & Thomson Limited | Construction | 2007 |
| O'Rourke Contracting PLC | Construction | 1980 |
| Oak Apple Landscapes Limited | Administrative & support | 2014 |
| Oak Barrels Ltd | Wholesale & retail | 2017 |
| Oak Bespoke Limited | Manufacturing | 2024 |
| Oak Croft (Bearsted) Management Company Limited | Households | 2007 |
| Oak Homes (Kent) Ltd | Construction | 2021 |
| Oak Meadow Farm Ltd | Manufacturing | 2023 |
| Oak MOT Centre Limited | Wholesale & retail | 2017 |
| Oak Tree Barn Events Limited | Hospitality | 2024 |
| Oakcrown Developments (Blake House) Limited | Construction | 2020 |
| Oakdene Newton Limited | Real estate | 2015 |
| Oakenhelm Ltd | Professional & scientific | 2025 |
| Oakenwood Limited | Administrative & support | 2014 |
| Oakes Pet Crematorium Limited | Professional & scientific | 2025 |
| Oakhive Carpet Contractors Limited | Administrative & support | 2002 |
| Oakko Ltd | Wholesale & retail | 2018 |
| Oaklawn Court Freehold Limited | Households | 2017 |
| Oaklawn Court Stanmore Management Company Limited | Households | 1984 |
| Oakleaf Electrical Contractors Ltd. | Construction | 1998 |
| Oakleaf Heating Ltd. | Construction | 1999 |
| Oakley Car & Classic Limited | Wholesale & retail | 2016 |
| Oakley Court RTM Company Limited | Households | 2013 |
| Oakley Maidstone Ltd | Wholesale & retail | 2022 |
| Oakley Motorcycles Limited | Wholesale & retail | 2020 |
| Oakmead Ltd | Construction | 2020 |
| Oaks Fencing & Landscaping Limited | Administrative & support | 2021 |
| Oaks Green Management (Bethersden) Limited | Households | 2022 |
| Oakspire Homes Ltd | Hospitality | 2025 |
| Oakt Services Limited | Professional & scientific | 2022 |
| Oaktree Consulting Services Limited | Professional & scientific | 2008 |
| Oaktree Properties Management Ltd | Real estate | 2023 |
| Oakwood Construction Services Limited | Construction | 2016 |
| Oakwood Maintenance & Facilities Ltd | Construction | 2025 |
| Oakwood Park Grammar School | Education | 2011 |
| Oakwood Park Medical Limited | Health & social care | 2026 |
| Oakwood Property Group Ltd | Construction | 2022 |
| Oakwood Specialist Training Limited | Education | 2007 |
| Oana Planning and Consultancy Limited | Professional & scientific | 2019 |
| Oasis Daily Homecare Ltd | Health & social care | 2024 |
| Oasis Vehicle Sales Limited | Wholesale & retail | 2016 |
| Oast Gardens (Warmlake) Limited | Households | 2022 |
| Oast Investments Limited | Construction | 1989 |
| Oatley & Overy Property Ltd | Real estate | 2011 |
| Oatmeals Ltd | Hospitality | 2022 |
| OB-3 Limited | Real estate | 2025 |
| OBA School Ltd | Education | 2011 |
| Obelisk Real Estate Ltd | Real estate | 2020 |
| Obey Ventures Ltd | Information & communication | 2016 |
| Obladi Oblada Ltd | Professional & scientific | 2021 |
| Oblix Sales Ltd | Wholesale & retail | 2026 |
| Obsidian Drive Ltd | Transport & logistics | 2026 |
| Obsidian Property Operations Ltd | Real estate | 2025 |
| Obvious Print Solutions Limited | Professional & scientific | 1999 |
| OCD Media Ltd | Professional & scientific | 2014 |
| Ocean Blue (Bournemouth) Ltd. | Real estate | 2011 |
| Ocean Harvest Technology Group PLC | Wholesale & retail | 2021 |
| Ocean Professionals UK Ltd | Transport & logistics | 2024 |
| Ocean Spices Trading Ltd | Wholesale & retail | 2025 |
| Oceanic Strategic Planning Limited | Transport & logistics | 2015 |
| Oculate Records Ltd | Information & communication | 2026 |
| Ocura Healthcare Furniture Limited | Extraterritorial | 2017 |
| Ocura Healthcare Ltd | Wholesale & retail | 2013 |
| Ocura Holdings Limited | Financial services | 2020 |
| Ocura Limited | Extraterritorial | 2017 |
| ODD JOB Hire Ltd | Administrative & support | 2025 |
| Odelia Group Ltd | Health & social care | 2023 |
| ODH Holdings Limited | Financial services | 2024 |
| Odilotid UK Limited | Information & communication | 2021 |
| Odin Security Group Ltd | Administrative & support | 2024 |
| Odyssey Estates Ltd | Real estate | 2021 |
| OEB2019 Limited | Professional & scientific | 2019 |
| OEG Resources Limited | Construction | 2016 |
| OFF Stage Strategies Limited | Public administration | 2024 |
| Office in a Box Systems Ltd | Construction | 2016 |
| Office Perfection Limited | Administrative & support | 2003 |
| Officelight Construction Ltd | Construction | 2017 |
| Offshore Marine Limited | Mining & quarrying | 2015 |
| Often Partisan Limited | Arts & recreation | 2022 |
| OG Waterproofing Ltd | Construction | 2026 |
| OGK Firm Limited | Wholesale & retail | 2025 |
| Ogo-Oluwa Global Ltd | Manufacturing | 2025 |
| Ogogo Entertainment Limited | Arts & recreation | 2012 |
| Ogogo Fitness Limited | Information & communication | 2023 |
| OGR Surfacing Ltd | Construction | 2021 |
| OGS Garden Services Ltd | Administrative & support | 2021 |