| NOW & Then Interiors Ltd | Wholesale & retail | 2010 |
| NOW Motors Limited | Wholesale & retail | 2024 |
| NOX Fire & Security Ltd | Professional & scientific | 2025 |
| Nozaloysious Limited | Transport & logistics | 2026 |
| Nrmn Ltd | Professional & scientific | 2019 |
| NS Mechanical Services Ltd | Construction | 2024 |
| Nsbs (UK) Limited | Construction | 2009 |
| NST Customs Ltd | Transport & logistics | 2020 |
| NSW Developments Ltd | Construction | 2004 |
| NT Micro Consulting Ltd | Health & social care | 2017 |
| NTP Developments Ltd | Construction | 2023 |
| NTP Plumbing and Heating Ltd | Construction | 2023 |
| Nude Laser Clinic Ltd | Other services | 2021 |
| Nude Property Group Ltd | Real estate | 2026 |
| Nude Skin Clinic Ltd | Other services | 2021 |
| Number Plate People Ltd | Wholesale & retail | 2022 |
| Nunnery Square Partnership | | 1994 |
| Nurite Industrial Supplies Limited | Wholesale & retail | 2000 |
| Nurse Naomi Ltd | Health & social care | 2024 |
| NUT NUT Denim Ltd | Wholesale & retail | 2026 |
| NW (York) Limited | Wholesale & retail | 2004 |
| Nwmw Holdings Ltd | Financial services | 2021 |
| Nxcontrol Ltd | Information & communication | 2020 |
| NXT Level Property Development Ltd | Real estate | 2024 |
| NY Racing Ltd | Arts & recreation | 2024 |
| Nyakundi UK Ltd | Health & social care | 2023 |
| Nyandorog Ltd | Manufacturing | 2025 |
| O & T Holdings Limited | Health & social care | 2024 |
| O.B Nails & Beauty Limited | Other services | 2026 |
| Oak Security Systems Limited | Administrative & support | 2010 |
| Oak Tree Park Management Ltd | Households | 2018 |
| Oakendale Building Solutions Ltd | Construction | 2019 |
| Oakendale Joinery Ltd | Construction | 2015 |
| Oaklands Development Management Company Limited | Households | 2022 |
| Oaklaw Limited | Construction | 2013 |
| Oakleaf Carpentry & Joinery Limited | Manufacturing | 2008 |
| Oakleigh Properties Ltd | Construction | 2025 |
| Oakley Interior Solutions Ltd | Construction | 2010 |
| Oakley Shopfitters Limited | Professional & scientific | 2019 |
| Oakleys Goods Ltd | Wholesale & retail | 2023 |
| Oakstedge Limited | Wholesale & retail | 2007 |
| Oakstedge Property Limited | Hospitality | 2020 |
| Oasis Developments Group Ltd | Construction | 2026 |
| Oasis Food S42 Ltd | Hospitality | 2025 |
| Oasis Payroll Services Limited | Professional & scientific | 2024 |
| Oasis Studio Group Limited | Information & communication | 2006 |
| Oasis Window Cleaning Ltd | Administrative & support | 2026 |
| OB Property Investments Limited | Administrative & support | 2016 |
| Obiageli Group Ltd | Other services | 2023 |
| OBO Packwood Estates Limited | Real estate | 2024 |
| OBR Group Limited | Administrative & support | 2025 |
| Obsessive Recessive Roots C.I.C. | Agriculture & fishing | 2025 |
| OCA Taxis Ltd | Transport & logistics | 2017 |
| Occasionall Staff Ltd | Extraterritorial | 2023 |
| Occasionapply Limited | Extraterritorial | 2025 |
| Ocean Crown Harrogate Ltd | Hospitality | 2020 |
| Ocean Fish Bar & Chinese Limited | Hospitality | 2020 |
| Ocean Services Limited | Extraterritorial | 1998 |
| Oceans Fins UK Limited | Wholesale & retail | 2026 |
| Ochiba Limited | Information & communication | 2005 |
| Octopus ATI Ltd | Wholesale & retail | 2019 |
| Oculi (Chesterfield) Ltd | Wholesale & retail | 2020 |
| Odot Promotions Limited | Arts & recreation | 2018 |
| Odyssey Restaurant Ltd | Hospitality | 2017 |
| OEM Tech Limited | Administrative & support | 2023 |
| OFF the Grid Training Facilites Limited | Arts & recreation | 2026 |
| OFF the Grid Training Limited | Arts & recreation | 2023 |
| Off-Road Developments Ltd | Wholesale & retail | 2020 |
| Office Brew Crew Ltd | Wholesale & retail | 2025 |
| Ofield & Sons Joinery Ltd | Manufacturing | 2024 |
| Ogilby Construction Limited | Construction | 1987 |
| Ogilby Property Services Limited | Real estate | 2025 |
| Oglum Ltd | Wholesale & retail | 2024 |
| Ohana's Coffee Ltd | Hospitality | 2026 |
| Ohmn Limited | Information & communication | 2026 |
| Oice Support Services Ltd | Health & social care | 2018 |
| OIL CAN Grooming Limited | Wholesale & retail | 2014 |
| OK Medical Limited | Health & social care | 2004 |
| Okrc Ltd | Health & social care | 2023 |
| Olatimmy Medics Limited | Health & social care | 2021 |
| Old Brampton Limited | Real estate | 2016 |
| Old Brampton Properties Ltd | Construction | 2014 |
| Old Cestrefeldians' Trust Limited | Education | 2014 |
| Old Orchard Nurseries Limited | Wholesale & retail | 2007 |
| Old School Taphouse Ltd | Hospitality | 2021 |
| Oldfield Farm Developments Limited | Construction | 2025 |
| Oldknow Contracting Limited | Construction | 2010 |
| OLI Bates Coaching Ltd | Other services | 2024 |
| Olive Cove Studio Limited | Other services | 2026 |
| Olive Gardens (Chesterfield) Management Company Limited | Extraterritorial | 2020 |
| Olive HBA Ltd | Other services | 2026 |
| Olive Landscapes Ltd | Administrative & support | 2026 |
| Olive Wellness Ltd | Health & social care | 2026 |
| Oliver Perez Limited | Professional & scientific | 2020 |
| OM Shivam Pictures Limited | Professional & scientific | 2024 |
| Omenai Limited | Health & social care | 2019 |
| Omicron Advisory LLP | | 2018 |
| Omnicomplexity Ltd | Information & communication | 2023 |
| ON Point Injection Services Ltd | Health & social care | 2022 |
| ON the Go Care Limited | Health & social care | 2016 |