| North Workshop Ltd | Wholesale & retail | 2016 |
| Northcourt Services Limited | Information & communication | 2007 |
| Northern Frozen Foods Ltd | Wholesale & retail | 2024 |
| Northrock Capital Ltd | Real estate | 2026 |
| Noruwa Investment Group Limited | Real estate | 2022 |
| Norway Gate 1-31 (ODD) RTM Company Limited | Households | 2006 |
| NOT Your Every Day Ltd | Administrative & support | 2021 |
| NOT Your Every Day Properties Ltd | Real estate | 2022 |
| NOU Range Ltd | Hospitality | 2025 |
| Novative Medical Ltd | Health & social care | 2011 |
| Noventris Ltd | Information & communication | 2011 |
| Novo Management Company (Oxford) Limited | Households | 2005 |
| NOW Nutrition Ltd | Wholesale & retail | 2020 |
| NOW Property Maintenance Ltd | Construction | 2025 |
| NOX Obscura Ltd | Wholesale & retail | 2025 |
| Nozzlenlace Ltd | Wholesale & retail | 2025 |
| NPL Commissioning Services Limited | Professional & scientific | 2017 |
| Npsych Limited | Health & social care | 2010 |
| Nrec Ltd | Real estate | 2021 |
| NRM UK & Ireland Chapter Vision 2040 Ltd | Other services | 2022 |
| NRS Maintenance Ltd | Construction | 2024 |
| Nsor Limited | Hospitality | 2024 |
| NST Roofing & Building Ltd | Construction | 2026 |
| Ntoiconstruction Ltd | Construction | 2023 |
| Nuba Consulting Limited | Information & communication | 2013 |
| Nubian Sanator Ltd | Health & social care | 2025 |
| Nucleotide Medical Limited | Health & social care | 2019 |
| Nuelson Limited | Health & social care | 2024 |
| Nuelss Business Consultant Limited | Information & communication | 2015 |
| Nuha Services Ltd | Professional & scientific | 2018 |
| NUI Tech Consultancy (UK) Ltd | Information & communication | 2021 |
| Number 117 Widmore Road Bromley Management Company Limited | Households | 2010 |
| Nuola Wigs Limited | Wholesale & retail | 2020 |
| Nurse Care by LOU Ltd | Health & social care | 2025 |
| Nuthan Mall Ltd | Health & social care | 2022 |
| Nuvevo Ltd | Information & communication | 2025 |
| Nuvola Solutions Limited | Information & communication | 2025 |
| Nvoka Healthcare Ltd | Health & social care | 2014 |
| Nwekene Healthcare Ltd | Health & social care | 2022 |
| NWT Property Services Ltd | Construction | 2021 |
| NXT LVL Scaffolding Limited | Construction | 2018 |
| Nxto Ltd | Information & communication | 2026 |
| NYB Services Limited | Professional & scientific | 2026 |
| NZS Construction Ltd | Construction | 2026 |
| O Electrical Services Ltd | Construction | 2024 |
| O&T Healthcare Limited | Health & social care | 2025 |
| O'Donovan Developments Limited | Real estate | 2016 |
| O'Jeda Services Limited | Health & social care | 2022 |
| O-I Bolivia Holdings Limited | Extraterritorial | 2015 |
| O.J. Jays Consult Limited | Administrative & support | 2017 |
| OAC IT Solutions Ltd | Information & communication | 2021 |
| Oadflsdet Ltd | Manufacturing | 2026 |
| Oak Hall Studios Ltd | Information & communication | 2020 |
| Oak+Acorns Healthcare Ltd | Wholesale & retail | 2024 |
| Oakes Padel Ltd | Education | 2026 |
| Oakfield Management Partners Limited | Professional & scientific | 2012 |
| Oakhill Chase (Crawley) Management Company Limited | Households | 2005 |
| Oakhill House Leaseholders Ltd | Households | 2023 |
| Oakland Orangeries and Garden Rooms Limited | Construction | 2008 |
| Oaklands Freehold Limited | Households | 2010 |
| Oaklands Rise Residents Company Limited | Households | 1994 |
| Oaklands Square Residents Management Company Limited | Households | 2012 |
| Oaks Court RTM Company Limited | Households | 2024 |
| Oaktree Gardens Limited | Real estate | 2005 |
| Oars and LEE, UK Ltd | Health & social care | 2021 |
| Oasis Hotel (Harlow) Limited | Hospitality | 1999 |
| OB1 Healthcare Services Limited | Health & social care | 2023 |
| Obaben Limited | Health & social care | 2022 |
| Obatof- G Limited | Health & social care | 2026 |
| Obesolutions Limited | Information & communication | 2018 |
| Obian Limited | Health & social care | 2012 |
| Objective HR Ltd | Professional & scientific | 2016 |
| OBK Synergy UK Ltd | Health & social care | 2022 |
| Obkay Shipping Ltd | Transport & logistics | 2026 |
| OCA Limited | Health & social care | 2021 |
| Ocad Ltd | Financial services | 2026 |
| Occucare Ltd | Health & social care | 2011 |
| Occur Ltd | Information & communication | 2017 |
| Ocean Hill Lodge Limited | Health & social care | 2023 |
| Ocean Ridge Limited | Health & social care | 2025 |
| Ocean Ridge Services Ltd | Professional & scientific | 2025 |
| Oceancapitalgb Ltd | Financial services | 2025 |
| Oceanic Resources International Consultancy Ltd | Administrative & support | 2023 |
| Oceanic Resources International Ltd | Administrative & support | 1996 |
| Ocena Ltd | Health & social care | 2025 |
| OCP Restaurant and Bakery Ltd | Wholesale & retail | 2025 |
| Octopus Express Limited | Hospitality | 2026 |
| Odelowo Limited | Information & communication | 2018 |
| Odogwu Medco Limited | Health & social care | 2019 |
| Odogwu Medical Ltd | Health & social care | 2010 |
| Odulaja Property Management Limited | Real estate | 2021 |
| Officevision Limited | Wholesale & retail | 1988 |
| Officialamazingglazing Ltd | Manufacturing | 2025 |
| Officialffl Ltd | Education | 2025 |
| OFI ADE Limited | Health & social care | 2023 |
| OG Square Limited | Real estate | 2020 |
| Ogadi Ltd | Health & social care | 2020 |
| Oganiru Ndigbo, Harlow Essex Ltd | Other services | 2021 |
| Ogigconsult Limited | Wholesale & retail | 2023 |
| OGK Ltd | Construction | 2015 |