| ON Road Haulage Ltd | Transport & logistics | 2021 |
| ON Site Service (UK) Limited | Manufacturing | 2003 |
| ON the Move 24 Ltd | Administrative & support | 2018 |
| ON the Rock Limited | Real estate | 2019 |
| ON the Scene Event Management Ltd | Professional & scientific | 2020 |
| ON the Shoulders of Giants Limited | Professional & scientific | 2002 |
| ON to the Next Travel Ltd | Administrative & support | 2025 |
| On-The-Go Auto Valet Limited | Administrative & support | 2025 |
| Onadan Butchery & Fishmongers Ltd | Wholesale & retail | 2025 |
| Onaf Limited | Other services | 2020 |
| Onamus Ltd | Real estate | 2024 |
| Oncscare Ltd | Information & communication | 2025 |
| Oncue Audio Services Ltd | Other services | 2026 |
| Onda Collective Limited | Wholesale & retail | 2025 |
| Ondina Services Ltd | Professional & scientific | 2022 |
| Onduty 24 Limited | Administrative & support | 2014 |
| One & One Projects | Real estate | 2020 |
| One 2 One Driving Academy Ltd | Education | 2025 |
| One and Seven Limited | Arts & recreation | 2008 |
| One ASH Investments Ltd | Professional & scientific | 2024 |
| One Barnsdale Ltd | Professional & scientific | 2013 |
| One Business Water Ltd | Water & waste | 2022 |
| One Church Leicester | Other services | 2016 |
| One Clear (Leicester) Limited | Water & waste | 2025 |
| One Click Crazy Deals Limited | Wholesale & retail | 2016 |
| One Click Estate Agents Limited | Real estate | 2024 |
| One Community ELY CIC | Other services | 2024 |
| One Diamond Consultancy Ltd | Professional & scientific | 2017 |
| One Digital Technologies Limited | Information & communication | 2017 |
| One Dose Limited | Wholesale & retail | 2015 |
| One Express Leicester Limited | Transport & logistics | 2022 |
| One Fabrication Ltd | Manufacturing | 2021 |
| One Fashion ( PVT) Ltd | Wholesale & retail | 2025 |
| One Green Spark Ltd | Manufacturing | 2022 |
| One Haus Ltd | Construction | 2020 |
| One Home Alliance Limited | Real estate | 2023 |
| One Hundred and Two Percent Ltd | Real estate | 2025 |
| One Immigration Ltd | Professional & scientific | 2008 |
| One Key Property Solutions Ltd | Real estate | 2019 |
| One MAN Renovations Limited | Construction | 2021 |
| One Midlands Limited | Professional & scientific | 2017 |
| One More Recruitment Limited | Administrative & support | 2023 |
| One One Zero Limited | Wholesale & retail | 2009 |
| One Root Limited | Professional & scientific | 2024 |
| One Safe Space Limited | Education | 2022 |
| One Small Step One Giant Leap Ltd | Information & communication | 2006 |
| One Solution (IMS) Limited | Construction | 2012 |
| One Source Ltd | Professional & scientific | 2023 |
| One Stitch Ltd | Manufacturing | 2021 |
| One Stop Cash & Carry Limited | Wholesale & retail | 2024 |
| One Stop Chai Ltd | Hospitality | 2020 |
| One Stop Dealers Limited | Wholesale & retail | 2019 |
| One Stop Pizza and Dessert Limited | Wholesale & retail | 2025 |
| One Stop Property Finance Ltd | Financial services | 2019 |
| One Structure Ltd | Wholesale & retail | 2026 |
| One Top Store Leicester Ltd | Wholesale & retail | 2025 |
| One Touch Enterprises Ltd | Information & communication | 2024 |
| One Trendz Ltd | Wholesale & retail | 2024 |
| One Utilities & Consultancy Limited | Administrative & support | 2012 |
| One Way Entertainment Limited | Arts & recreation | 2015 |
| One-Hd Limited | Wholesale & retail | 2025 |
| ONE.7MIL&CO Ltd | Real estate | 2014 |
| Oneapex Solutions UK Ltd | Transport & logistics | 2026 |
| Onebowl Limited | Hospitality | 2018 |
| Onebrick Properties Limited | Real estate | 2017 |
| Oneclick Essentials Ltd | Wholesale & retail | 2019 |
| Onegrp Ltd | Construction | 2025 |
| Oneiro Properties Limited | Real estate | 2025 |
| Onemoreroom (Leicester) Ltd | Professional & scientific | 2023 |
| Onenationuk Ltd | Arts & recreation | 2026 |
| Onepoint Consult Ltd | Information & communication | 2026 |
| Oner Oncer Ltd | Professional & scientific | 2020 |
| Onesixeight: Fitness Ltd | Arts & recreation | 2024 |
| ONESOLUT1ON Ltd | Construction | 2025 |
| Onesource Proprietor Ltd. | Real estate | 2020 |
| Onestep Community Care Group Limited | Health & social care | 2024 |
| Onestop Women Health Clinic Ltd | Health & social care | 2022 |
| ONG 1 Ltd | Professional & scientific | 2024 |
| ONG 2 Ltd | Professional & scientific | 2024 |
| ONG Energy Ltd | Financial services | 2022 |
| ONG Holdco Ltd | Financial services | 2022 |
| ONG Operations Ltd | Professional & scientific | 2022 |
| ONG Optical Ltd | Health & social care | 2022 |
| ONG Residential Ltd | Real estate | 2022 |
| ONG Traded Businesses Ltd | Financial services | 2022 |
| ONG Yorkshire Ltd | Construction | 2023 |
| Ongarmart Ltd | Wholesale & retail | 2022 |
| Onggi Ltd | Hospitality | 2015 |
| ONI Enterprises Ltd | Real estate | 2024 |
| Onidoc Ltd | Health & social care | 2010 |
| Onkar Care Home Limited | Real estate | 2003 |
| Onkar Developments Limited | Real estate | 2018 |
| Online Estate Agents Ltd | Real estate | 2015 |
| Online Garage Ltd | Wholesale & retail | 2025 |
| Online Health & Wellness Services Coaching Ltd | Other services | 2025 |
| Online Inc Solutions Ltd | Professional & scientific | 2014 |
| Online Property Marketing Ltd | Real estate | 2020 |
| Online Skin Ltd | Extraterritorial | 2018 |
| Online UK Brands Ltd | Wholesale & retail | 2024 |
| Only Army Ltd | Other services | 2014 |