| Nottswide Logistics Ltd | Transport & logistics | 2023 |
| Nova Drive Trade Ltd | Wholesale & retail | 2026 |
| Nova Music and Arts Ltd | Administrative & support | 2025 |
| Noval Services Ltd | Wholesale & retail | 2017 |
| Novalex Trading Ltd | Wholesale & retail | 2025 |
| Novus Grid Limited | Energy | 2024 |
| Novus Mechanical Services Ltd | Construction | 2024 |
| NRC Cosmetic Limited | Other services | 2009 |
| NS Holiday Lodge Ltd | Hospitality | 2020 |
| NSA Power Solutions Ltd | Construction | 2026 |
| NSG Driveways Ltd | Construction | 2026 |
| Nsquare Clean and Secure Ltd | Administrative & support | 2026 |
| NT Motorhomes Ltd | Wholesale & retail | 2020 |
| NTS K9 Services UK Ltd | Other services | 2021 |
| Nuask Limited | Wholesale & retail | 2023 |
| Nubeo Ltd | Information & communication | 2025 |
| Nubu Group Limited | Real estate | 2021 |
| Numbers on Track Ltd | Professional & scientific | 2025 |
| Nutlless Ltd | Manufacturing | 2026 |
| Nutrition Eatery Ltd | Hospitality | 2026 |
| Nvable Holdings Limited | Financial services | 2019 |
| NW Financial Solutions Limited | Financial services | 2003 |
| Nwapez Property Maintenance and Services Limited | Construction | 2020 |
| Nù-Yéw Therapeutic Spa Ltd | Other services | 2024 |
| O&J Transport Ltd | Transport & logistics | 2019 |
| O'Brian-Laurie Limited | Professional & scientific | 2022 |
| O-G Psychotherapy Ltd | Health & social care | 2025 |
| O.S Ware Ltd | Information & communication | 2025 |
| Oak Bank Manor Management Ltd | Administrative & support | 2004 |
| Oak Lodge Consulting Limited | Professional & scientific | 2024 |
| Oakham Assets Limited | Real estate | 2024 |
| Oakham Beauty Ltd | Health & social care | 2023 |
| Oakham Commercial Ltd | Real estate | 2019 |
| Oakham Construction Services Limited | Construction | 2017 |
| Oakham Electrical Services Ltd | Construction | 2014 |
| Oakham Residential Ltd | Real estate | 2024 |
| Oakham Suite Limited | Hospitality | 2009 |
| Oakhams Limited | Construction | 2015 |
| Oaklight Group Ltd | Manufacturing | 2025 |
| Oakmont Search Group Ltd | Administrative & support | 2026 |
| Oakwell Cars Ltd | Wholesale & retail | 2013 |
| Oasis Children Service Group Limited | Health & social care | 2026 |
| OB Logistics Ltd | Wholesale & retail | 2020 |
| Objectsoft Limited | Information & communication | 1998 |
| Obsessions Ladies Fashion Limited | Wholesale & retail | 2022 |
| Occasions Express Limited | Wholesale & retail | 2022 |
| Occlusal Management Limited | Health & social care | 2007 |
| OD Mansfield 18 Limited | Hospitality | 2025 |
| ODD FOX Ltd | Extraterritorial | 2014 |
| Oddsockloc Ltd. | Wholesale & retail | 2018 |
| Odra Grocery Store Ltd | Wholesale & retail | 2025 |
| Odysia Cruise Limited | Extraterritorial | 2025 |
| Odysia Limited | Extraterritorial | 2025 |
| OEL Properties Ltd | Real estate | 2026 |
| Offensive Wear Ltd | Wholesale & retail | 2020 |
| Office Essentials Interiors LLP | | 2008 |
| OG Parry Ltd | Administrative & support | 2022 |
| Ogfrust Limited | Professional & scientific | 2015 |
| Ogleystudios Ltd | Wholesale & retail | 2026 |
| Ohannes Burger Mansfield Ltd | Hospitality | 2025 |
| Ohannes Food Solutions Ltd | Hospitality | 2019 |
| Ohdata Ltd | Information & communication | 2026 |
| Ohso Cherry Limited | Information & communication | 2018 |
| Oilcare Ltd | Wholesale & retail | 2008 |
| Oilfield Strategic Solutions Ltd | Mining & quarrying | 2013 |
| Oiza Healthcare Limited | Real estate | 2016 |
| OJ Hobson Ltd | Administrative & support | 2022 |
| OK Convenience Store Limited | Wholesale & retail | 2022 |
| Okiki Limited | Real estate | 2022 |
| Okodoko Ltd | Wholesale & retail | 2024 |
| Okoro African Shop Ltd | Wholesale & retail | 2025 |
| Oldrock Consulting Limited | Information & communication | 2015 |
| Olgabakedthat Ltd | Manufacturing | 2023 |
| Olilau Ltd | Real estate | 2025 |
| Olive Studio Mansfield Ltd | Other services | 2026 |
| Olive Tree Escapes Ltd | Hospitality | 2024 |
| Olive Tree Kitchen Ltd | Hospitality | 2019 |
| Oliver Brown Holdings Ltd | Financial services | 2022 |
| Oliver Brown Limited | Agriculture & fishing | 2008 |
| Oliver Kenny IT Consulting Ltd | Information & communication | 2017 |
| Olivest Ltd | Real estate | 2021 |
| Olmacmovements Ltd | Transport & logistics | 2020 |
| Oloriperfumes Ltd | Wholesale & retail | 2025 |
| Oltu Ltd | Transport & logistics | 2020 |
| Oluwatoyin Oladeji Limited | Health & social care | 2024 |
| Olympus Leisure Limited | Other services | 2026 |
| Omega Health and Performance Ltd. | Arts & recreation | 2017 |
| Omega Windows and Doors Limited | Construction | 2015 |
| Omni Concierge Services Limited | Other services | 2003 |
| Omni Renovations Limited | Construction | 2026 |
| Omnis Electrical Limited | Manufacturing | 2015 |
| ON ALL Pawz Dog Grooming Ltd | Other services | 2022 |
| ON ALL Pawz Ltd | Wholesale & retail | 2020 |
| ON ALL Pawz Pet Supplies Ltd | Wholesale & retail | 2022 |
| ON Craig Ltd | Administrative & support | 2022 |
| Ondarmzoin Ltd | Wholesale & retail | 2021 |
| One 4 Design Ltd | Professional & scientific | 2013 |
| One Call Roofing & Maintenance Limited | Construction | 2025 |
| One Click Components Limited | Wholesale & retail | 2018 |
| One Hundred Stars Design Limited | Construction | 2019 |