| Npnd Ltd | Construction | 2022 |
| NPT AI Technologies Ltd | Information & communication | 2026 |
| NPV Projects Limited | Professional & scientific | 1998 |
| Nrmp Consultancy Ltd | Financial services | 2021 |
| NRV Traders Ltd | Wholesale & retail | 2024 |
| NTA GAS Heating & Plumbing Services Ltd | Construction | 2019 |
| NTM Trading Ltd | Wholesale & retail | 2022 |
| Ntranklin Limited | Health & social care | 2023 |
| Number One Interiors Ltd | Construction | 2015 |
| Number Plate Tech Ltd | Wholesale & retail | 2025 |
| Numero Holdings Ltd | Financial services | 2026 |
| Nuno Logistics Ltd | Transport & logistics | 2025 |
| Nupendo Ltd | Health & social care | 2019 |
| NUR Aesthetics Clinic Ltd | Other services | 2024 |
| Nurain Ltd | Health & social care | 2023 |
| Nursangels Ltd | Other services | 2014 |
| Nurture Solutions Ltd | Wholesale & retail | 2019 |
| NUS47 Ltd | Hospitality | 2022 |
| NVP Expert Ltd | Construction | 2025 |
| NWT Energy Ltd | Construction | 2020 |
| NWT International Limited | Wholesale & retail | 2002 |
| NWT Solar Ltd | Construction | 2020 |
| Nyanchama Limited | Professional & scientific | 2023 |
| Nyla Care Ltd | Health & social care | 2025 |
| Nyland Aesthetics Limited | Other services | 2018 |
| O&J Assets Ltd | Financial services | 2021 |
| O&J Lettings Ltd | Real estate | 2021 |
| O&J Partners Ltd | Administrative & support | 2021 |
| O'Brien Properties Limited | Construction | 1973 |
| O'Hagan & Bell Ltd | Hospitality | 2007 |
| O'Made Care Ltd | Administrative & support | 2024 |
| Oak Computing Services Limited | Information & communication | 1999 |
| Oak Cottage (Crawley) Management Company Limited | Real estate | 2016 |
| Oak PUB Group Limited | Hospitality | 2026 |
| Oakapple Holdings Limited | Financial services | 2024 |
| Oakes Mcgill Limited | Extraterritorial | 2021 |
| Oakhurst Groundworks Limited | Construction | 2019 |
| Oakmore Consulting Limited | Administrative & support | 2024 |
| Oakvero Construction Ltd | Construction | 2026 |
| Oakwood Furniture Ltd | Wholesale & retail | 2026 |
| OAN Tours Ltd | Transport & logistics | 2017 |
| OAT Energy Ltd | Information & communication | 2023 |
| Objective Developers Limited | Construction | 2017 |
| Objective Studio Limited | Professional & scientific | 2004 |
| Objectware Limited | Manufacturing | 1991 |
| Oblique Limited | Real estate | 2002 |
| Observit Ltd | Administrative & support | 2004 |
| Obyquity Ltd | Health & social care | 2013 |
| Occd Ltd | Administrative & support | 2020 |
| Ocean Azzurro Limited | Real estate | 2025 |
| Ocean Investments Limited | Real estate | 2025 |
| Ocean Wave Logistics Ltd | Transport & logistics | 2026 |
| Odysseys Travel Limited | Administrative & support | 2024 |
| OEC (Electrical) Ltd | Construction | 2017 |
| OF Property Investments Limited | Real estate | 2023 |
| Officefile Limited | Administrative & support | 2002 |
| Ofuza Ltd | Wholesale & retail | 2026 |
| Ogebra Limited | Professional & scientific | 2025 |
| OH Accounting Limited | Professional & scientific | 2023 |
| Oisel Productions Limited | Information & communication | 2026 |
| Olaitan Limited | Wholesale & retail | 2026 |
| Old Christchurch Limited | Real estate | 2015 |
| Old Girls Play TOO CIC | Education | 2026 |
| Old Martyrs (Management) Limited | Households | 1998 |
| Old School House Crawley RTM Company Limited | Households | 2025 |
| Oldlands Farmhouse Ltd | Hospitality | 2019 |
| Olibradley Ltd | Extraterritorial | 2024 |
| Olisa Investments Ltd | Real estate | 2021 |
| Olive Home and Solar Solutions Ltd | Construction | 2026 |
| Olive Home Care & Support Limited | Administrative & support | 2015 |
| Oliver Van Thiel Limited | Professional & scientific | 2021 |
| Oliwier Online Ltd | Wholesale & retail | 2016 |
| Ollis Creative Limited | Professional & scientific | 2015 |
| Omarrows Ltd | Wholesale & retail | 2022 |
| OMC Group Ltd | Real estate | 2023 |
| OMD Engineering Limited | Manufacturing | 2010 |
| OMF Fitness Ltd | Arts & recreation | 2026 |
| OMF Ltd | Other services | 2021 |
| OMJ Electrical Services Limited | Construction | 2022 |
| OMJ Maintenance Services Limited | Extraterritorial | 2022 |
| Omnicart Limited | Extraterritorial | 2024 |
| ON Q Engineering Services Ltd | Information & communication | 2013 |
| ON the Board Ltd | Information & communication | 2021 |
| ON the Level (UK) Limited | Manufacturing | 2004 |
| ON the Rock (HR) Ltd | Administrative & support | 2025 |
| ON the Ropes Ltd | Wholesale & retail | 2011 |
| On-Site Car Body Repairs Ltd | Wholesale & retail | 2026 |
| On-Site Limited | Construction | 1994 |
| One Check Ltd | Extraterritorial | 2017 |
| One House Live Ltd. | Other services | 2016 |
| One Park ROW Limited | Construction | 2026 |
| One Portfolio Management Limited | Construction | 2003 |
| One Resourcing Ltd | Transport & logistics | 2006 |
| One Step Transport Solutions Ltd | Transport & logistics | 2020 |
| One Stop 15 Limited | Manufacturing | 2016 |
| One Stop Joinery Limited | Manufacturing | 2004 |
| Onesafeadult Ltd | Professional & scientific | 2026 |
| Oneweld Supplies Ltd | Construction | 2021 |
| Oneworld Security Ltd | Administrative & support | 2022 |
| Online Agora Limited | Wholesale & retail | 2024 |