| Nomoli Holdings (Roydon) Limited | Construction | 2024 |
| Norman Living Ltd | Real estate | 2023 |
| North Hertfordshire and District Citizens Advice Bureau | Public administration | 2001 |
| North Herts Asphalte (Roofing) Limited | Construction | 1966 |
| North Herts Electrical Limited | Extraterritorial | 2016 |
| North Herts Fitting Centre Holdings Limited | Manufacturing | 1996 |
| North Herts Properties Ltd | Real estate | 2021 |
| North Herts Sparks Ltd | Construction | 2022 |
| North-Herts Translations & Interpretation Services Ltd | Professional & scientific | 2025 |
| Northill Consulting Ltd | Information & communication | 2022 |
| Northland Controls Letchworth Ltd | Real estate | 2017 |
| Northland Controls Limited | Information & communication | 2007 |
| Northstarlog Ltd | Transport & logistics | 2025 |
| Norton Heating and Plumbing Utility Services Ltd | Construction | 2013 |
| Norton Studio Conservation Architects Limited | Professional & scientific | 2023 |
| Norwood Green(Block A)Management Company Limited | Households | 1985 |
| Nothing Sounds Good Limited | Wholesale & retail | 2025 |
| Notice Real Estate Limited | Real estate | 2021 |
| Novafox Ltd | Information & communication | 2024 |
| November Labs Limited | Information & communication | 2015 |
| Novikin Ltd | Health & social care | 2014 |
| Npnp Ltd | Financial services | 2021 |
| Npro Investments 2 Limited | Extraterritorial | 2024 |
| NS Tech Solutions Limited | Administrative & support | 2014 |
| Number 54 Advisory Limited | Administrative & support | 2026 |
| Number Goes UP Ltd | Information & communication | 2024 |
| Oak Commercial (London Colney) Ltd | Financial services | 2025 |
| Oak Commercial Ltd | Construction | 2020 |
| Oak Developments (Bedfordshire) Limited | Construction | 2010 |
| Oak Developments Holdings Ltd | Financial services | 2020 |
| Oak View Property Development Ltd | Real estate | 2022 |
| Oakley Arboriculture Limited | Administrative & support | 2022 |
| Observa Ltd | Information & communication | 2026 |
| OCE Risley Limited | Energy | 2025 |
| OCE Skelton Limited | Energy | 2025 |
| Ocean Surveying Ltd | Construction | 2024 |
| Odiliaclark Ltd | Public administration | 2018 |
| Odraga Holding Ltd | Financial services | 2024 |
| OEE Property Consultancy Ltd | Real estate | 2021 |
| OF the Pear Tree Ltd | Information & communication | 2024 |
| Ohene Limited | Professional & scientific | 2025 |
| Olatbol Consulting Ltd | Transport & logistics | 2026 |
| Olympus Solar II Ltd | Energy | 2023 |
| Omega Cohost Ltd | Administrative & support | 2025 |
| Omnicaretech Limited | Administrative & support | 2025 |
| ON Your Travels Ltd | Administrative & support | 1996 |
| On-Chain Services Ltd | Information & communication | 2022 |
| On-Systems Limited | Administrative & support | 2011 |
| One Degree Development Ltd | Professional & scientific | 2015 |
| One Seven Events Ltd | Professional & scientific | 2020 |
| One Two One Property Service Limited | Real estate | 2025 |
| ONE2ONERECORDING Ltd | Information & communication | 2015 |
| Onedeploy Limited | Information & communication | 2015 |
| Only Renters in the Building Limited | Real estate | 2025 |
| Onpro Limited | Information & communication | 2013 |
| Opaluke Limited | Arts & recreation | 2025 |
| Open Art Box CIC | Education | 2019 |
| Operam Limited | Professional & scientific | 2012 |
| Operation Profits Limited | Information & communication | 2023 |
| Optimal Technologies Holdings Limited | Financial services | 2016 |
| Optimal Technologies Limited | Manufacturing | 1997 |
| Orchard Close (Stanstead Abbots) Management Company Limited | Households | 1993 |
| Orchard Grove (Chalvey Grove) Management Company Limited | Households | 2004 |
| Orchard Park Gardens Management Limited | Households | 2005 |
| Orchard Rose Developments Ltd | Construction | 2022 |
| Orchestra (Leighton) Limited | Construction | 2025 |
| OS Nagra Ltd | Construction | 2014 |
| Overdrive Haulage & Transport Limited | Transport & logistics | 2024 |
| Ovolo Books Limited | Information & communication | 2000 |
| Ovpd 6 Ltd | Real estate | 2022 |
| Ovpd 6A Ltd | Real estate | 2022 |
| Ovpd 6B Ltd | Real estate | 2022 |
| Oxen Installations Ltd | Information & communication | 2024 |
| P & M Trading and Consultancy Limited | Manufacturing | 2024 |
| P&W Engineering Ltd | Professional & scientific | 2026 |
| P.A.R. Estates Limited | Extraterritorial | 1993 |
| P2D2 Group Limited | Financial services | 2020 |
| Pacefit Limited | Wholesale & retail | 2017 |
| Padgett TM Ltd | Construction | 2024 |
| Pan-African Diaspora Initiatives (Padi) CIC | Administrative & support | 2026 |
| Pandom Solutions Ltd | Construction | 2025 |
| Paola Uttaro Events Limited | Other services | 2014 |
| Park House Investments Limited | Real estate | 2016 |
| Parker Aviation Ltd | Manufacturing | 2025 |
| Parkmain Properties Limited | Real estate | 1997 |
| Pascut Limited | Manufacturing | 2017 |
| Pattersa Property Limited | Real estate | 2025 |
| Pattie Pantall Coaching Ltd | Professional & scientific | 2019 |
| Pavetesting Limited | Manufacturing | 2003 |
| Pavetestinggroup Limited | Manufacturing | 2017 |
| Pawesome Walking Fields Ltd | Real estate | 2024 |
| Pcbi Ltd | Professional & scientific | 2002 |
| Peach Threads Ltd | Wholesale & retail | 2025 |
| Pear Group Ltd. | Administrative & support | 2015 |
| Pearlafrobraidsuk Limited | Other services | 2025 |
| Pearljay Consulting Limited | Professional & scientific | 2017 |
| Penguin Insurance Services Limited | Financial services | 2011 |
| Pepper Rafferty Limited | Information & communication | 2010 |
| Perfect Choice Education Consultants Limited | Education | 2022 |
| Perishable Freight Consultants Limited | Transport & logistics | 2018 |