| Notus Contract Lifting Ltd | Administrative & support | 2019 |
| Notus Industrial Services Limited | Financial services | 2023 |
| Notus Management Services LLP | | 2025 |
| Notus Site Services Limited | Professional & scientific | 2025 |
| Notus Storage Limited | Transport & logistics | 2024 |
| Nova Auditing Ltd | Professional & scientific | 2013 |
| Nova Consulting (UK) Ltd | Extraterritorial | 2014 |
| Nova Flame Limited | Professional & scientific | 2025 |
| Novamont Solutions Ltd | Professional & scientific | 2026 |
| NPN Healthcare Limited | Health & social care | 2025 |
| NSI Design Ltd | Other services | 2014 |
| NSM Kent - Services Ltd | Transport & logistics | 2024 |
| NU U 2 Limited | Other services | 2012 |
| Nuclear NDT Ltd | Professional & scientific | 2013 |
| Nurhat Investments Ltd | Real estate | 2017 |
| Nutrition Victor Ltd | Manufacturing | 2013 |
| Nuudesweats Ltd. | Wholesale & retail | 2026 |
| NVY Beauty Ltd | Other services | 2025 |
| Nyojwando Ltd | Health & social care | 2022 |
| Nystrom Property Limited | Construction | 2010 |
| Nzouaks Ltd | Health & social care | 2025 |
| O'Connell's Drywall Contractors Limited | Construction | 2003 |
| O'Connell's Properties (Kent) Limited | Real estate | 2018 |
| O-Ug Ltd | Financial services | 2020 |
| OAD Street Events Limited | Hospitality | 2020 |
| OAD Street Food and Crafts Limited | Hospitality | 2017 |
| Oaff Limited | Information & communication | 2019 |
| Oak Design and Build Limited | Construction | 2025 |
| Oak Tree Carpentry Limited | Construction | 2022 |
| Oak&Hammer Woodcraft Ltd | Manufacturing | 2024 |
| Oakdene Management Limited | Hospitality | 1980 |
| Oakgold Ventures Limited | Arts & recreation | 2001 |
| Oakleaf Digital Ltd | Administrative & support | 2024 |
| Oakmont Prestige Capital Investments Limited | Real estate | 2023 |
| Oakmont Prestige Limited | Construction | 2018 |
| Oaks Care Holdings Ltd | Health & social care | 2022 |
| Oakstead Holdings Limited | Real estate | 2025 |
| Oast Commercial Ltd | Wholesale & retail | 2020 |
| Oast Osteopathy Limited | Health & social care | 2014 |
| Oast Wellbeing Ltd | Health & social care | 2019 |
| Obaomo & Co Limited | Wholesale & retail | 2025 |
| Oberrson Group Limited | Financial services | 2023 |
| Oblongata Limited | Information & communication | 2022 |
| Ocean Garments & Alterations Ltd | Other services | 2026 |
| Odyssey Finance Ltd | Financial services | 2000 |
| OG Plants Ltd | Wholesale & retail | 2019 |
| OGC Rage Rooms Ltd | Arts & recreation | 2025 |
| Ogen Holdings Limited | Real estate | 2025 |
| OJ Cutz Ltd | Other services | 2024 |
| OK Family Heritage Ltd | Real estate | 2025 |
| Okaao Services Limited | Other services | 2019 |
| Okamgba Limited | Professional & scientific | 2022 |
| Okestra Consulting Ltd | Information & communication | 2012 |
| Okiss Services Limited | Health & social care | 2021 |
| Olabab Services UK Ltd | Construction | 2015 |
| Old HAY Farms Limited | Transport & logistics | 1990 |
| Old Mill Cafe Limited | Hospitality | 2021 |
| Old Oast Engineering Ltd | Professional & scientific | 2026 |
| Old Place Farm Limited | Real estate | 1999 |
| Old Town Stores Limited | Wholesale & retail | 2003 |
| Oleg Transport Limited | Transport & logistics | 2025 |
| Olis HAY Kent Limited | Construction | 2020 |
| Oliver Reeve & Partners Limited | Financial services | 2004 |
| Olivina Building Services Limited | Construction | 2016 |
| Olivina Limited | Wholesale & retail | 2006 |
| Oluwabukola Danmusa Ltd | Health & social care | 2021 |
| Oluwafunke Medical Limited | Health & social care | 2022 |
| Omo-Ekun Records Limited | Information & communication | 2023 |
| Omograce Excelsior Limited | Hospitality | 2017 |
| ON Building Limited | Construction | 2003 |
| ON Coach Services Limited | Transport & logistics | 2000 |
| One Bar Limited | Hospitality | 2012 |
| One Foot in the Grape Ltd | Hospitality | 2019 |
| One OIL Broking Limited | Professional & scientific | 2021 |
| Onespace Fitness Limited | Arts & recreation | 2026 |
| Ongley Construction Ltd | Construction | 2025 |
| Ontop Building Solutions Limited | Construction | 2019 |
| OPC Telematics Ltd | Information & communication | 2025 |
| Oppsedge Advisory Ltd | Real estate | 2026 |
| Opticablue Limited | Professional & scientific | 2013 |
| Optima Alarms Limited | Manufacturing | 2023 |
| Optima Security Systems Limited | Manufacturing | 1988 |
| Optima-Coaching Ltd | Other services | 2025 |
| Oral Arts Laboratory Ltd | Manufacturing | 2016 |
| Orange Brushes Ltd | Wholesale & retail | 2025 |
| Orchard View Residents Management Company Limited | Households | 2023 |
| Ordinarily Different Ltd | Professional & scientific | 2017 |
| Oregen Computer Training (U.K.) Limited | Information & communication | 1992 |
| Oriri Ltd | Wholesale & retail | 2025 |
| Orivo Supply Ltd | Wholesale & retail | 2023 |
| Ormilia Holdings Ltd | Real estate | 2026 |
| Orzola Fire Limited | Public administration | 2020 |
| Osler & Faraday Limited | Professional & scientific | 1988 |
| Osteopathy and Sports Injury Clinic Ltd | Health & social care | 2022 |
| OUR Community Multi Academy Trust | Education | 2017 |
| OUR Training Club Ltd | Arts & recreation | 2026 |
| Ouse Contract Services Limited | Administrative & support | 2023 |
| Ouse Firewood Ltd | Wholesale & retail | 2025 |
| OUT of Hours Marketing Ltd | Professional & scientific | 2024 |
| OUT to the Woods CIC | Education | 2021 |