| Onaux Ltd | Wholesale & retail | 2025 |
| Onbasi Limited | Hospitality | 2025 |
| Onblackheath 2017 Limited | Arts & recreation | 2017 |
| Once a Year Limited | Professional & scientific | 2013 |
| Once WE Were Warriors Ltd | Information & communication | 2023 |
| Onceloved Limited | Wholesale & retail | 2025 |
| Oncologist Mohan Ltd | Health & social care | 2024 |
| Oncorps Limited | Information & communication | 2016 |
| One Aptus Ltd | Real estate | 2023 |
| One Berkeley Crescent Freehold Company Limited | Households | 2022 |
| One Big Circle Ltd | Information & communication | 2017 |
| One Big Family (O.B.F) CIC | Hospitality | 2021 |
| One Big Field Ltd | Administrative & support | 2009 |
| One Blenheim Road Management (Bristol) Limited | Extraterritorial | 1979 |
| One Blue World Ltd | Construction | 2024 |
| One Bristol Curriculum Ltd | Information & communication | 2021 |
| One Bristol Limited | Real estate | 2024 |
| One Call Roofing Solutions Ltd | Construction | 2022 |
| One Capital Consult Ltd | Information & communication | 2025 |
| One Care (Bnssg) C.I.C. | Health & social care | 2016 |
| One Care Consulting & Services Limited | Information & communication | 2019 |
| One Care General Practice Delivery Limited | Health & social care | 2025 |
| One Click Tile UK Limited | Construction | 2019 |
| One Cycle Ltd | Administrative & support | 2017 |
| One Day Business Intelligence Ltd | Information & communication | 2025 |
| One Family Law Ltd | Professional & scientific | 2023 |
| One Fibre Ltd | Information & communication | 2018 |
| One Fifty Enterprises Ltd | Construction | 2018 |
| One for ALL Alliance | Education | 2025 |
| One Glenfrome Road Management Company Limited | Real estate | 2022 |
| One Green Kitchen C.I.C. | Hospitality | 2022 |
| One Guarantee Limited | Financial services | 2017 |
| One Holding Investments Ltd | Real estate | 2007 |
| One Hundred Estates Limited | Real estate | 2010 |
| One JC Ltd | Real estate | 2021 |
| One Life Left Ltd | Arts & recreation | 2016 |
| One Like That Ltd | Real estate | 2022 |
| One Love Bar & Takeaway Ltd | Hospitality | 2018 |
| One More Pizza Limited | Hospitality | 2025 |
| One More Saga Productions Ltd | Arts & recreation | 2025 |
| One More Than Four Ltd | Professional & scientific | 2017 |
| One New Thing BTN Limited | Professional & scientific | 2019 |
| One North Street Limited | Households | 2000 |
| One Oakfield Place Clifton Management Co. Limited | Households | 2001 |
| One Pacifica Ltd | Households | 2024 |
| One Pence Productions Limited | Arts & recreation | 2015 |
| One Picture Limited | Other services | 1994 |
| One Planet Matters CIC | Professional & scientific | 2018 |
| One Plus UNO Ltd | Professional & scientific | 2026 |
| One Pool & Spa Limited | Construction | 2020 |
| One Quote Direct Insurance Services Limited | Financial services | 2005 |
| One Rosemary Lane Ltd | Health & social care | 2019 |
| One Scientific Limited | Professional & scientific | 1999 |
| One Step at a Time Ltd | Professional & scientific | 2008 |
| One Stop Essentials Ltd | Wholesale & retail | 2025 |
| One Stop Letting.Com Limited | Administrative & support | 2009 |
| One Surveying Limited | Administrative & support | 2017 |
| One Touch Computer Services Ltd | Extraterritorial | 2008 |
| One Touch Switching DOT COM Limited | Information & communication | 2023 |
| One UP Supplies Limited | Wholesale & retail | 2024 |
| One Vision Health Ltd | Information & communication | 2009 |
| One Waterside (Bath) Management Company Limited | Households | 2025 |
| One Zero Two Consulting Ltd | Information & communication | 2010 |
| ONE25 Limited | Health & social care | 1997 |
| ONE2ONE Design Group Ltd | Manufacturing | 2019 |
| ONE50STUDIO Ltd | Professional & scientific | 2017 |
| ONE80DENTAL Limited | Health & social care | 2018 |
| Onechristison Limited | Financial services | 2024 |
| Onecycle Energy Limited | Professional & scientific | 2021 |
| Onecycle Magno Ltd | Manufacturing | 2018 |
| Onecycle Noble Metals Ltd | Professional & scientific | 2017 |
| Onefusion Ltd | Professional & scientific | 2021 |
| Onemilliondotuk Ltd | Professional & scientific | 2021 |
| Onen HAG OLL (UK) Ltd | Other services | 2015 |
| Onepoint Software Ltd | Information & communication | 2021 |
| Onesevenseven Holdings Limited | Other services | 2020 |
| Oneshortword Ltd | Professional & scientific | 2022 |
| Onestopmoneymanager Ltd | Administrative & support | 2009 |
| Oneway Services Limited | Arts & recreation | 2006 |
| Onewing Management Ltd | Real estate | 2026 |
| Onfinity Holdings Limited | Financial services | 2025 |
| Onfinity Limited | Information & communication | 2014 |
| Ongandu Limited | Information & communication | 2022 |
| Onhealth Limited | Health & social care | 2013 |
| ONI Group Limited | Wholesale & retail | 2025 |
| Onieni Limited | Health & social care | 2018 |
| Oninfive Ltd | Information & communication | 2026 |
| Oniques Services Limited | Professional & scientific | 2008 |
| Onis Legal Services Ltd | Professional & scientific | 2024 |
| ONJ Ltd | Construction | 2014 |
| Onka Consults Ltd | Professional & scientific | 2024 |
| Onkadtech Limited | Information & communication | 2014 |
| Onley Prison Services Limited | Public administration | 1998 |
| Online Block Management.Com Ltd | Households | 2013 |
| Online British School Limited | Education | 2019 |
| Online Coating Limited | Manufacturing | 1990 |
| Online Dating Limited | Information & communication | 2010 |
| Online Finance Expert Ltd | Information & communication | 2010 |
| Online Gifts UK Ltd | Wholesale & retail | 2019 |
| Online Study Solutions Ltd | Information & communication | 2021 |