| NSN Retail Ltd | Wholesale & retail | 2024 |
| NSS Property Limited | Real estate | 2024 |
| Nssa (Holdings) Limited | Real estate | 2022 |
| Nsst Construction Ltd | Administrative & support | 2022 |
| NST Cars Ltd | Wholesale & retail | 2024 |
| NST Global Limited | Real estate | 2013 |
| NT Real Estate Ltd | Real estate | 2026 |
| NTD Production Ltd | Real estate | 2020 |
| Nukilik Designs Ltd | Information & communication | 2015 |
| Number 1 ALL in One Builder Ltd | Construction | 2012 |
| NUMBERS2GO Ltd | Wholesale & retail | 2023 |
| Numerise Analytics Ltd | Administrative & support | 2016 |
| NUR Food Centre Ltd | Other services | 2023 |
| NUR Global Limited | Professional & scientific | 2019 |
| Nutra Life Healthcare Limited | Wholesale & retail | 2024 |
| Nutrabright Ltd | Wholesale & retail | 2024 |
| Nutrition and YOU Ltd | Public administration | 2020 |
| Nutrizpaw Ltd | Wholesale & retail | 2026 |
| Nuve Transfers Ltd | Transport & logistics | 2025 |
| Nuvia House Ltd | Health & social care | 2025 |
| NV Builder & Roofing Ltd | Construction | 2025 |
| NVS Design and Build Ltd | Construction | 2021 |
| NXP Tech Limited | Wholesale & retail | 2021 |
| Nxtpxl Productions Ltd. | Information & communication | 2015 |
| NY Investment London Ltd | Construction | 2024 |
| NYY Build Ltd | Real estate | 2022 |
| NZ & Co Property Management Ltd | Real estate | 2024 |
| NZ Bays Manuka Limited | Wholesale & retail | 2026 |
| Nzurisana Limited | Information & communication | 2015 |
| O & D Electric Bikes Ltd | Wholesale & retail | 2024 |
| O & I Consulting Limited | Professional & scientific | 2009 |
| O & S Construction Limited | Construction | 2026 |
| O Battersby Earthworks Ltd | Construction | 2026 |
| O D T (Europe) Limited | Information & communication | 1991 |
| O'Gabriel Haulage Ltd | Transport & logistics | 2013 |
| Oaken Lane (Claygate) Management Company Limited | Households | 1999 |
| Oakley Management Enterprises Ltd | Health & social care | 2013 |
| Oakmount Ventures Ltd | Other services | 2023 |
| Oakstone Builders Ltd | Construction | 2026 |
| Oakswood Ltd | Real estate | 2020 |
| Oakville Realty Ltd | Construction | 2020 |
| Oanta Brickwork Ltd | Construction | 2025 |
| Oasis Homecare Services Ltd | Health & social care | 2018 |
| Oasis Services London Limited | Information & communication | 2016 |
| Obelisk Camberley Limited | Real estate | 2017 |
| Obeto Optics Limited | Health & social care | 2023 |
| Oblige Global Limited | Information & communication | 2017 |
| Obsidian Gold Ltd | Real estate | 2025 |
| Obtainable Fitness UK Ltd | Other services | 2023 |
| Ocean City Food Ltd | Hospitality | 2018 |
| Ocean Home Private Ltd | Construction | 2024 |
| Ocean Spark Cleaning Ltd | Administrative & support | 2025 |
| Oceanmasters Logistics Ltd | Transport & logistics | 2024 |
| Octillion 1048 Limited | Administrative & support | 2017 |
| Octmarux Limited | Education | 2007 |
| Octo Investment Limited | Real estate | 2011 |
| Oddjob FX Limited | Professional & scientific | 2017 |
| Offplatform.Io Ltd | Professional & scientific | 2026 |
| Offshade Ltd | Wholesale & retail | 2025 |
| Ogaden Productions Ltd | Professional & scientific | 2026 |
| OH My Golly Gosh Ltd | Professional & scientific | 2024 |
| Ohii Deep Tiler Limited | Construction | 2025 |
| OIL of the Throne Limited | Manufacturing | 2019 |
| Ojobins Limited | Health & social care | 2011 |
| Ojohn Haulage Ltd | Transport & logistics | 2016 |
| Okafor Interbiz Ltd | Construction | 2018 |
| Oklahomas Electric Ltd | Energy | 2019 |
| Olaabul Limited | Health & social care | 2019 |
| Old Tree Joinery Ltd | Construction | 2022 |
| Oldbury Express Limited | Wholesale & retail | 2014 |
| OLI and RAK Ltd | Wholesale & retail | 2025 |
| OLI Electric Ltd | Construction | 2021 |
| Olimax Property Ltd | Real estate | 2019 |
| Olive Comms Ltd | Information & communication | 2021 |
| Olive Tree Nursery & Community Centre CIC | Health & social care | 2025 |
| Oliver Gilbody Art Ltd | Arts & recreation | 2019 |
| OLO Bolo Ltd | Real estate | 2022 |
| OLO OLO Ltd | Real estate | 2022 |
| Olou Limited | Real estate | 2016 |
| OM Enviroment Ltd | Professional & scientific | 2024 |
| OM Logistics Ltd | Transport & logistics | 2025 |
| OM Tutors Ltd | Education | 2021 |
| OMF Surgery Ltd | Health & social care | 2021 |
| Omkar Construction Services Ltd | Construction | 2020 |
| Omkar Developers Ltd | Construction | 2024 |
| Omkar Homes Limited | Real estate | 2025 |
| Omnilink Logistics Limited | Transport & logistics | 2026 |
| Omnio Ltd | Wholesale & retail | 2025 |
| Omnivo Limited | Wholesale & retail | 2026 |
| Omns Properties Ltd | Real estate | 2024 |
| OMS Trades Limited | Hospitality | 2024 |
| ON Air 24 Ltd | Information & communication | 2014 |
| ON Flow Construction Ltd | Construction | 2019 |
| ON Nuage Limited | Information & communication | 2018 |
| ON SET Electrics Ltd | Construction | 2025 |
| ON the Go Ltd | Information & communication | 2013 |
| ON Time Scaffolding Ltd | Construction | 2016 |
| Once Education Group Ltd | Administrative & support | 2023 |
| One & Only Cafe Ltd | Wholesale & retail | 2023 |
| One Click Finance Limited | Financial services | 2020 |