| Nysa Fortune Ltd | Financial services | 2026 |
| Nysh UK Ltd | Transport & logistics | 2024 |
| Nytram Agents Limited | Administrative & support | 2016 |
| Nyuk Limited | Financial services | 2023 |
| Nzee Motor Repairs Ltd | Manufacturing | 2024 |
| O & C Group Ltd | Administrative & support | 2023 |
| O & J Enterprises Ltd | Hospitality | 2025 |
| O C (MK) Limited | Professional & scientific | 2021 |
| O RAN Test Ltd | Professional & scientific | 2026 |
| O'Brien Aircraft Services Limited | Manufacturing | 2017 |
| O'Briens Bottle Shop Limited | Hospitality | 2020 |
| O'Cansey Ltd | Information & communication | 2019 |
| O'Connell Global Enterprises Ltd | Financial services | 2025 |
| O'Foodi Foods Ltd | Hospitality | 2021 |
| O'Leary Engineering Ltd | Professional & scientific | 2018 |
| O'Leary Holdings Ltd | Real estate | 2024 |
| O'Lis Global Limited | Administrative & support | 2026 |
| O'Neill Coating Services Limited | Manufacturing | 2009 |
| O'Tutu Associates Limited | Professional & scientific | 2022 |
| O'Tutu Transport Limited | Transport & logistics | 2023 |
| O-Sde Enterprise Ltd | Wholesale & retail | 2023 |
| O.B's Consult Ltd | Health & social care | 2025 |
| OAA Business Services Limited | Professional & scientific | 2013 |
| OAD Group Ltd | Professional & scientific | 2026 |
| Oak Beauty Solutions Ltd | Other services | 2026 |
| Oak Bookkeeping Services Limited | Professional & scientific | 2025 |
| Oak Factor (Milton Keynes) Ltd | Manufacturing | 2019 |
| Oak House Design & Build Ltd | Construction | 2019 |
| Oak Sanctuary Limited | Administrative & support | 2018 |
| Oak Tree Car Valeting Centre Ltd | Administrative & support | 2024 |
| Oak Tree House Engineering Services Limited | Professional & scientific | 2021 |
| Oak Vale Property Solutions Limited | Administrative & support | 2023 |
| Oakdale Electrical Contractors Limited | Construction | 2012 |
| Oake Branch Limited | Administrative & support | 2003 |
| Oakes Hardware Limited | Wholesale & retail | 2018 |
| Oakesen Limited | Real estate | 2014 |
| Oakgold Limited | Transport & logistics | 2005 |
| Oakgrove (Milton Keynes) Residents Management Company Limited | Real estate | 2012 |
| Oakgrove Medicare Limited | Health & social care | 2024 |
| Oakhill Court Management Company (Milton Keynes) Limited | Real estate | 1988 |
| Oakhill Resources Management Limited | Administrative & support | 2024 |
| Oakhill Voice Solutions Limited | Information & communication | 2016 |
| Oakk Cargo Ltd | Wholesale & retail | 2023 |
| Oakkay Property Investments Limited | Real estate | 2024 |
| Oakland Pride Limited | Wholesale & retail | 1988 |
| Oakleigh Estate & Properties Limited | Real estate | 2021 |
| Oakleigh Flooring Limited | Wholesale & retail | 2008 |
| Oakleigh SAS Consultancy Limited | Information & communication | 2013 |
| Oakline Trees & Fencing Ltd | Administrative & support | 2025 |
| Oakmonds Estates Ltd | Households | 2022 |
| Oakpine Media Ltd | Information & communication | 2026 |
| Oakridge Fresh Limited | Hospitality | 2025 |
| Oakridge MK Limited | Health & social care | 2017 |
| Oakridge Park Barns Management Limited | Real estate | 2015 |
| Oakroyal Limited | Real estate | 1993 |
| Oakshire Homes Ltd | Construction | 2015 |
| Oakspire Care Limited | Health & social care | 2026 |
| Oakstonemarket Ltd | Wholesale & retail | 2026 |
| Oaktide Clinical Limited | Professional & scientific | 2026 |
| Oakwood Associates Limited | Professional & scientific | 2020 |
| Oakwood Property Surveys Limited | Professional & scientific | 2012 |
| OAL Consulting Ltd | Professional & scientific | 2018 |
| Oasia Holding Company Limited | Administrative & support | 2022 |
| Oasislink Technologies Ltd | Wholesale & retail | 2026 |
| Oats Health Care Services Ltd | Health & social care | 2024 |
| OAUACCTNG2001 Ltd | Other services | 2025 |
| OBA Couture UK Limited | Manufacturing | 2024 |
| Obamacare Properties Ltd | Real estate | 2018 |
| OBD Pro Ltd | Information & communication | 2025 |
| OBE Property Solutions Ltd | Real estate | 2025 |
| Obelisk Property Limited | Real estate | 2022 |
| Obeslindiwe Limited | Health & social care | 2015 |
| OBI Design Ltd | Information & communication | 2024 |
| Obiino Medical Consultancy Limited | Health & social care | 2005 |
| Obocks Ltd | Professional & scientific | 2012 |
| Obrems Global Logistics Ltd | Wholesale & retail | 2026 |
| Obscura Vault Limited | Wholesale & retail | 2025 |
| Obscure Solutions (UK) Limited | Information & communication | 2003 |
| Obscure Solutions Limited | Information & communication | 1999 |
| Obsidian House Studios Limited | Manufacturing | 2018 |
| OC Build Ltd | Financial services | 2019 |
| Ocando Ltd | Real estate | 2019 |
| Occupational Audiometry Ltd | Professional & scientific | 2020 |
| Occupational Rehab Limited | Health & social care | 2002 |
| OCD Design Limited | Information & communication | 2007 |
| OCD Fresh Finishing Limited | Wholesale & retail | 2019 |
| Ocean 77 Ltd | Hospitality | 2022 |
| Ocean Aquatic Design Ltd | Wholesale & retail | 2012 |
| Ocean Beauty Ltd | Other services | 2023 |
| Ocean Care Shipping PVT Ltd | Transport & logistics | 2024 |
| Ocean Digital Marketing Limited | Information & communication | 2026 |
| Ocean Overseas Holdings Limited | Professional & scientific | 1957 |
| Ocean Print & Design Limited | Manufacturing | 2006 |
| Ocean Protection Services Limited | Administrative & support | 2011 |
| Ocean Risk Dynamics Limited | Professional & scientific | 2026 |
| Ocean Support Ltd | Professional & scientific | 2021 |
| Ocean Transport Ltd | Transport & logistics | 2019 |
| Ocean&K Accountancy UK Limited | Professional & scientific | 2018 |
| Oceanet 2000 Limited | Information & communication | 1998 |
| OCG Consultants Limited | Professional & scientific | 2020 |