| NUTRIK9 Limited | Wholesale & retail | 2021 |
| Nutrition & Catering Services Limited | Hospitality | 2019 |
| Nutrition Works Limited | Manufacturing | 2011 |
| Nutriwin UK Limited | Professional & scientific | 2025 |
| Nutthorpe Limited | Professional & scientific | 2015 |
| Nuvaire Ltd | Information & communication | 2025 |
| Nuvanta Capital Limited | Real estate | 2025 |
| Nuvia Properties Ltd | Real estate | 2025 |
| Nuview Solutions Ltd | Administrative & support | 2025 |
| Nuvision Biotherapies Limited | Manufacturing | 2015 |
| NV Social Limited | Professional & scientific | 2022 |
| NV Tattoo Limited | Other services | 2005 |
| NVD Properties Ltd | Real estate | 2021 |
| NVE Consulting Limited | Professional & scientific | 2014 |
| NVH Fleet Solutions Limited | Administrative & support | 2025 |
| NVQ Trainees Ltd | Education | 2020 |
| Nvrc Limited | Wholesale & retail | 2025 |
| NW Financial Services Limited | Financial services | 2017 |
| Nwande Limited | Health & social care | 2022 |
| NWB Holdings Limited | Financial services | 2021 |
| Nwdp Ltd | Real estate | 2023 |
| NWK Design Ltd | Information & communication | 2014 |
| Nwuli Limited | Health & social care | 2013 |
| Nxice Ltd | Wholesale & retail | 2025 |
| NXT Aequitas Ltd | Professional & scientific | 2022 |
| NXT Drive Limited | Wholesale & retail | 2025 |
| NXT GEN Capital Holdings Ltd | Financial services | 2024 |
| NXT Group Holdings Ltd | Financial services | 2022 |
| NXT REP Ltd | Manufacturing | 2026 |
| Nxtgen Learning Ltd | Professional & scientific | 2020 |
| Nxtlevel Scaffolding Ltd | Construction | 2020 |
| Nyakawino Express Limited | Health & social care | 2015 |
| Nyakecho Ltd | Health & social care | 2020 |
| Nyall Michael Humphreys Limited | Administrative & support | 2019 |
| Nyasa Premier Healthcare Services Ltd | Health & social care | 2021 |
| Nyawekie Private Limited | Health & social care | 2016 |
| Nyika Consulting Ltd | Professional & scientific | 2026 |
| Nylah Homes Limited | Other services | 2020 |
| Nynx Creatives Ltd | Information & communication | 2020 |
| NYO Studios Ltd | Administrative & support | 2024 |
| Nyota Destinations Ltd | Administrative & support | 2015 |
| Nytrex Worldwide Products Limited | Administrative & support | 2003 |
| Nyvej Co Ltd | Professional & scientific | 2024 |
| NZ Harris Ltd | Administrative & support | 2022 |
| NZ Properties Limited | Real estate | 2020 |
| NZB Property Specialists Limited | Households | 2016 |
| Nzime Limited | Professional & scientific | 2001 |
| Nzymes Limited | Professional & scientific | 1996 |
| O & N Enterprises Limited | Wholesale & retail | 2022 |
| O & N Oral Health Care Limited | Health & social care | 2008 |
| O Boyce Services Limited | Other services | 2023 |
| O J Engineering Services Ltd | Manufacturing | 2025 |
| O Johnston & Co Ltd | Professional & scientific | 2025 |
| O&B Beauty Lounge Ltd | Other services | 2024 |
| O&E Designs Limited | Manufacturing | 2022 |
| O&O Inns Ltd | Hospitality | 2019 |
| O'Connell Liam 81469 Limited | Transport & logistics | 2014 |
| O'Hara Insurance Services Limited | Financial services | 2003 |
| O'Hara Property Services Limited | Real estate | 2006 |
| O'Hara Sligo Limited | Financial services | 2016 |
| O'Heochaidh Ltd | Professional & scientific | 2025 |
| O'Jay OIL and GAS Ltd | Mining & quarrying | 2025 |
| O'Keeffe Building Services Limited | Construction | 2003 |
| O'Lala Nails & Beauty Limited | Other services | 2022 |
| O'Neill Gordon Global Limited | Professional & scientific | 2026 |
| O.H.Footitt Agricultural & Property Ltd | Agriculture & fishing | 2024 |
| O.M Energy Assessments Ltd | Professional & scientific | 2022 |
| O.M.K Investments Ltd | Real estate | 2024 |
| O.M.K. Healthcare Ltd | Administrative & support | 2010 |
| O.N Plastering Services Ltd | Construction | 2026 |
| O.T. Electrical Limited | Construction | 2005 |
| O3NOVATE UK Ltd | Professional & scientific | 2012 |
| O6K Limited | Professional & scientific | 2021 |
| O7 Drum Project Limited | Education | 2025 |
| OAD Discount Limited | Wholesale & retail | 2005 |
| OAE Construction Limited | Construction | 2020 |
| Oak 1855 Ltd | Hospitality | 2025 |
| Oak AOA Ltd | Health & social care | 2018 |
| Oak Castle Developments Limited | Construction | 2017 |
| Oak Cottage Enterprises Limited | Agriculture & fishing | 2003 |
| Oak Dental Laboratories Limited | Manufacturing | 1999 |
| Oak Hill House (Management) Company Limited | Households | 2013 |
| Oak House Advisory Limited | Professional & scientific | 2015 |
| Oak Leaf Creations Limited | Wholesale & retail | 2017 |
| Oak MSP Ltd | Information & communication | 2022 |
| Oak Overlays Ltd | Manufacturing | 2024 |
| Oak Property Investments Limited | Real estate | 1999 |
| Oak Public House Limited | Hospitality | 2023 |
| Oak Services Nottinghamshire Limited | Real estate | 2014 |
| Oak SO Simple Ltd | Wholesale & retail | 2023 |
| Oak Stairs Cladding System Ltd | Manufacturing | 2016 |
| Oak Technology Solution Ltd | Information & communication | 2023 |
| Oak Tree Alpacas Limited | Agriculture & fishing | 2020 |
| Oak Tree Court (Tollerton) Limited | Real estate | 2010 |
| Oak Tree Meadows Ltd | Real estate | 2023 |
| Oak Tree Motor Homes Limited | Manufacturing | 2004 |
| Oakbridge Home Care Ltd | Health & social care | 2026 |
| Oakbridge Housing CIC | Real estate | 2025 |
| Oakbrook Finance Limited | Professional & scientific | 2011 |
| Oakbrook Holdings (UK) Limited | Financial services | 2021 |