| Onboard Sport Psychology Ltd | Health & social care | 2024 |
| Oncoverge Consulting Limited | Health & social care | 2025 |
| Onda Trading Ltd | Wholesale & retail | 2023 |
| One Call Preston Limited | Wholesale & retail | 2017 |
| One Community Cleanup CIC | Health & social care | 2024 |
| One Day Ventures Limited | Real estate | 2024 |
| One Express Transport Ltd | Transport & logistics | 2020 |
| One Five One Collectibles Ltd | Wholesale & retail | 2023 |
| One Healthsource Limited | Health & social care | 2011 |
| One Investments Limited | Financial services | 2022 |
| One IT Service Consulting Limited | Information & communication | 2019 |
| One More Espresso Ltd | Information & communication | 2025 |
| One More One Less Ltd | Wholesale & retail | 2020 |
| One Mythic Grading Ltd | Wholesale & retail | 2024 |
| One of the Family Ltd | Health & social care | 2021 |
| One Percent Performance Ltd | Wholesale & retail | 2025 |
| One Residence Limited | Administrative & support | 2010 |
| One Square One Limited | Wholesale & retail | 2020 |
| One Stop Auto Levy Ltd | Other services | 2025 |
| One Stop Retail Ltd | Wholesale & retail | 2011 |
| One Stop Services (NW) Ltd | Manufacturing | 2020 |
| One Stop Shop Enterprise Limited | Wholesale & retail | 2020 |
| One Stop Shop Retail Ltd | Hospitality | 2020 |
| One Stop Travel Group Ltd | Administrative & support | 2025 |
| One Stop Travel Ltd | Administrative & support | 2017 |
| One Stop Van Hire and Sales Ltd | Wholesale & retail | 2025 |
| One Stop Warehouse (Bolton) Ltd | Wholesale & retail | 2025 |
| One Technical Limited | Information & communication | 2012 |
| One TEN Enterprises Ltd | Wholesale & retail | 2026 |
| One to ALL Limited | Wholesale & retail | 2021 |
| One Touch Security Ltd | Wholesale & retail | 2022 |
| One UP PPC Limited | Professional & scientific | 2019 |
| Oneclick Retail Limited | Wholesale & retail | 2026 |
| Onedoteleven Limited | Information & communication | 2013 |
| Oneeditionx Ltd | Wholesale & retail | 2026 |
| Onefancy Ltd | Wholesale & retail | 2019 |
| Oneil 2022 Limited | Financial services | 2022 |
| Onepot (Lancs) Limited | Real estate | 2023 |
| Onestop Motorworks Ltd | Wholesale & retail | 2026 |
| Oneup Talent Limited | Professional & scientific | 2026 |
| Oneup Tech Ltd | Wholesale & retail | 2021 |
| Oneyellow Limited | Professional & scientific | 2023 |
| Onit Entertainment Ltd | Information & communication | 2026 |
| Onliflux Ltd | Wholesale & retail | 2025 |
| Online Co. Marketing Ltd | Other services | 2017 |
| Online Customer Solutions Ltd | Wholesale & retail | 2023 |
| Online Part Worn Tyres Limited | Wholesale & retail | 2024 |
| Online Teaching Resources Ltd | Education | 2010 |
| Online Training Club Ltd | Arts & recreation | 2025 |
| Onlinefarmshop Ltd | Wholesale & retail | 2014 |
| Onlinemoto Limited | Wholesale & retail | 2017 |
| Only Auctions Ltd | Wholesale & retail | 2026 |
| Only Gems Ltd | Wholesale & retail | 2025 |
| ONM Limited | Wholesale & retail | 2018 |
| ONN Gard Ltd | Wholesale & retail | 2026 |
| Onpoint Trading Ltd | Construction | 2023 |
| Onsec FM Ltd | Financial services | 2021 |
| Onshore Technical Consultancy Limited | Professional & scientific | 2025 |
| Onside Youth Zones | Education | 2008 |
| Ontime Travel Ltd | Administrative & support | 2013 |
| Ontrak Services Ltd | Manufacturing | 2015 |
| Onway Services Ltd | Transport & logistics | 2026 |
| Onway Transport Ltd | Transport & logistics | 2025 |
| Onyx 1 Limited | Real estate | 2017 |
| Onyx PDA Limited | Professional & scientific | 2020 |
| Onyx Refinery Ltd | Wholesale & retail | 2025 |
| Onyx Tax & Advisory Ltd | Professional & scientific | 2026 |
| Oodles and Doodles Limited | Wholesale & retail | 2022 |
| Ooyes Ltd | Real estate | 2023 |
| OPA Engineering Solutions Limited | Manufacturing | 2017 |
| Opal Ceramics Limited | Health & social care | 2015 |
| Opconsult Limited | Information & communication | 1999 |
| Opec Housing LLP | | 2011 |
| Open Air Bounce Limited | Arts & recreation | 2025 |
| Open Financial Advice Ltd | Financial services | 2023 |
| Open Golf and Leisure Limited | Arts & recreation | 1987 |
| Open Golf Group Limited | Extraterritorial | 2007 |
| Open Golf Limited | Extraterritorial | 2000 |
| Open House Bolton Ltd | Real estate | 2021 |
| Open Journey Limited | Agriculture & fishing | 2018 |
| OPEN2SERVE Ltd | Wholesale & retail | 2020 |
| Openbook Solutions Limited | Professional & scientific | 2023 |
| Openly Legal Limited | Professional & scientific | 2026 |
| Openpro Ltd | Professional & scientific | 2019 |
| Operable Limited | Information & communication | 2022 |
| Operation Calm 2025 Community Interest Company | Other services | 2025 |
| Operion Limited | Information & communication | 2026 |
| Opia-Goodthinking Limited | Real estate | 2008 |
| Opiac Care Group Ltd | Administrative & support | 2020 |
| Opie (HC) Limited | Financial services | 2022 |
| Opie (PM) Limited | Real estate | 2022 |
| Opie (Prop Co) Limited | Real estate | 2022 |
| Opisthodom Holdings Ltd. | Information & communication | 2024 |
| OPM Universal Limited | Professional & scientific | 2021 |
| Opop Services Limited | Professional & scientific | 2018 |
| Opportune Limited | Information & communication | 2002 |
| OPS Leyland Limited | Construction | 2021 |
| Optaris Limited | Wholesale & retail | 2026 |
| Optibi Capital Limited | Administrative & support | 2021 |
| Optical Clarity Ltd | Health & social care | 2015 |