| Nrgi Construction Ltd | Construction | 2024 |
| NS Construction (Surrey) Limited | Construction | 2021 |
| Nsmdigital Limited | Information & communication | 2018 |
| Nstk Investments Ltd | Other services | 2022 |
| Nsure Estate Agents Ltd | Real estate | 2004 |
| Nsure Estate Planning Services Limited | Professional & scientific | 2001 |
| Nsure Financial Services Limited | Financial services | 1998 |
| Nsure Group Limited | Professional & scientific | 2002 |
| Nsure IT Ltd | Extraterritorial | 2004 |
| Nsure Security Limited | Professional & scientific | 2001 |
| NTM Stove Installations and Property Maintenance Ltd | Construction | 2022 |
| NTV Ltd | Information & communication | 2018 |
| Nufashion Ltd | Information & communication | 2022 |
| Nugget Investments Ltd | Real estate | 2020 |
| Number 18 Ltd | Professional & scientific | 2021 |
| Number 7 Brunswick Terrace Hove Limited | Households | 1969 |
| Nuovo Properties Limited | Real estate | 2019 |
| Nupost Consulting Limited | Administrative & support | 2012 |
| Nurturing Hope & Wellbeing Limited | Other services | 2023 |
| Nuserve Group Limited | Professional & scientific | 2012 |
| Nutbourne Nursery Limited | Agriculture & fishing | 2010 |
| Nutfetcher Films Ltd | Information & communication | 2015 |
| Nutra Stat (UK) Limited | Administrative & support | 1994 |
| Nuts & Volts Ltd | Wholesale & retail | 2023 |
| Nuvera Haus Beauty Ltd | Other services | 2025 |
| Nuvera Haus Studios Ltd | Other services | 2024 |
| Nuvista Ltd | Professional & scientific | 2025 |
| NVV Express Limited | Wholesale & retail | 2023 |
| NWP Goalkeeping Ltd | Wholesale & retail | 2026 |
| O'Donoghue Homes Limited | Real estate | 2023 |
| O'Hagan Brickwork Limited | Construction | 2018 |
| O'Sullivan Family Law Ltd | Professional & scientific | 2010 |
| O'Sullivan Solutions Ltd | Administrative & support | 2012 |
| O2 (Europe) Limited | Information & communication | 2001 |
| O2 (UK) Limited | Information & communication | 1986 |
| O2 Oak Limited | Information & communication | 1998 |
| O2 Pine Limited | Information & communication | 2007 |
| O2 Willow Limited | Information & communication | 2007 |
| Oak Strong Enterprises Ltd | Financial services | 2022 |
| Oakdale Construction (Southern) Limited | Construction | 2009 |
| Oaklands (Ferring) Limited | Households | 2014 |
| Oaklands Ferring Residents Ltd | Households | 2022 |
| Oakley Young Logistics Ltd | Transport & logistics | 2025 |
| Oakling UK Limited | Construction | 2022 |
| Oakthorpe House Ltd | Financial services | 2021 |
| Oakview Leisure Four Limited | Real estate | 2020 |
| Oakview Leisure One Limited | Real estate | 2020 |
| Oakview Leisure Parks Limited | Other services | 2020 |
| Oakwood Construction & Carpentry Limited | Construction | 2017 |
| Oakwood Tree Consultants Ltd. | Professional & scientific | 2006 |
| Oanas Ltd | Professional & scientific | 2015 |
| Oasis Empire Limited | Administrative & support | 2007 |
| Oasis Lending LLP | | 2016 |
| Oberholzer Properties Limited | Real estate | 2018 |
| Obsidian Begelly Ltd | Construction | 2024 |
| Obsidian Developments Ltd | Construction | 2020 |
| Obsidian Holdings Limited | Financial services | 2021 |
| Obvious Recruitment Ltd | Administrative & support | 2023 |
| OC International - UK | Other services | 2003 |
| Ocean 3S RTM Company Limited | Households | 2021 |
| Ocean House Holdings Limited | Construction | 2021 |
| Ocean Vets Ltd | Professional & scientific | 2016 |
| Oceanedge Cleaning Services Limited | Administrative & support | 2024 |
| Oceanic Pools and Spas Ltd | Arts & recreation | 2026 |
| Oceanside Leisure Limited | Hospitality | 2021 |
| OCH Group Limited | Construction | 2023 |
| Ockham Healthcare Limited | Administrative & support | 2015 |
| Ockham Liveries Ltd | Administrative & support | 2019 |
| Octheatrical Ltd | Arts & recreation | 2018 |
| Octigan Limited | Real estate | 2008 |
| Octopod Innovations Ltd | Information & communication | 2025 |
| Octopus Associates Limited | Professional & scientific | 2024 |
| Odin Global Limited | Administrative & support | 2016 |
| OF the Sea Ltd | Arts & recreation | 2025 |
| OFF Fields Sport Consulting Limited | Professional & scientific | 2009 |
| OFF Mains Solutions Limited | Administrative & support | 2023 |
| OFF Piste Properties Limited | Professional & scientific | 2010 |
| OFF White Media Ltd | Information & communication | 2018 |
| Offbeat BBQ Events Ltd | Hospitality | 2021 |
| Office Acoustix Limited | Professional & scientific | 2013 |
| Offington Consultancy Services Limited | Professional & scientific | 2024 |
| Offington Land Surveys Limited | Professional & scientific | 1999 |
| Offington Plumbing Services Limited | Construction | 2011 |
| Offington RTM Company Limited | Households | 2011 |
| Offside Productions Media Ltd | Information & communication | 2013 |
| OG EYE Health Ltd | Health & social care | 2018 |
| OGJ Limited | Professional & scientific | 2012 |
| OH Social Saints Ltd | Professional & scientific | 2023 |
| Ohana Projects Ltd | Construction | 2020 |
| Ohla Property Management Ltd | Real estate | 2021 |
| Oils & Grains Europe Limited | Extraterritorial | 2012 |
| OJH Bathrooms Limited | Construction | 2019 |
| OK OKI Limited | Wholesale & retail | 2013 |
| Okie Ltd | Manufacturing | 2005 |
| Old Barn Farm Business Park Limited | Real estate | 2018 |
| Old Fort Club Limited(The) | Extraterritorial | 1965 |
| Oldbuilders Ltd | Construction | 2018 |
| Olga Hamilton Nutrition Ltd | Health & social care | 2019 |
| Olitrades Ltd | Wholesale & retail | 2024 |
| Olive Branch Design Ltd. | Information & communication | 2014 |