| OF Romford Ltd | Hospitality | 2023 |
| OFF Trend Ltd | Administrative & support | 2024 |
| Office FIX Ltd | Construction | 2023 |
| OG Automotives Limited | Wholesale & retail | 2024 |
| OG Group Construction Ltd | Construction | 2024 |
| Ogada Limited | Wholesale & retail | 2024 |
| Oghenovo Enterprises Limited | Health & social care | 2019 |
| OH My Mylar Ltd | Wholesale & retail | 2024 |
| OH! Sea Moss Limited | Manufacturing | 2025 |
| OHH Foods Limited | Hospitality | 2018 |
| Ohlory Limited | Real estate | 2016 |
| Oilfusion Limited | Manufacturing | 2025 |
| OJA ASO Ltd | Information & communication | 2025 |
| OJM Property Maintenance Ltd | Construction | 2023 |
| OK Building & Construction Ltd | Construction | 2025 |
| Oken Group Ltd | Hospitality | 2025 |
| Okiki Consultancy Ltd | Professional & scientific | 2018 |
| Okna EKO Limited | Manufacturing | 2021 |
| OLA Partners Ltd | Professional & scientific | 2024 |
| Olade Ltd | Other services | 2026 |
| Oladebo Company Limited | Health & social care | 2020 |
| Olafusioladimeji Limited | Financial services | 2024 |
| Olak Limited | Health & social care | 2013 |
| Olakt Limited | Other services | 2012 |
| Olamiwale Services Ltd | Transport & logistics | 2020 |
| Olaoluwaolufemi Ltd | Construction | 2019 |
| Olaru Plastering Ltd | Construction | 2024 |
| Olat Solution's Ltd | Wholesale & retail | 2014 |
| Old & Newt Limited | Information & communication | 2014 |
| Old Kent After-School Club Ltd | Health & social care | 2026 |
| Old Line Ltd | Wholesale & retail | 2018 |
| Old Money Academy Ltd | Education | 2025 |
| Old Oakhouse Ltd | Extraterritorial | 2008 |
| Old Pond House Ltd | Households | 2020 |
| Olea Sportswear Ltd | Wholesale & retail | 2025 |
| Oleg & SON Ltd | Construction | 2022 |
| Oleg Construction Ltd | Construction | 2026 |
| Olesea Hair Studio Ltd | Other services | 2026 |
| Olive Accounting Limited | Professional & scientific | 2017 |
| Olive Mount Properties Ltd | Construction | 2024 |
| Oliver Gold Agencies Limited | Administrative & support | 2015 |
| Oliver Ventures Ltd | Information & communication | 2011 |
| Oliver's Construction Limited | Construction | 2024 |
| Oliver’S Safety NET Ltd | Professional & scientific | 2025 |
| Olivia MAE Marketing Ltd | Professional & scientific | 2021 |
| Olivia Rose Bridal & Eveningwear Limited | Wholesale & retail | 2010 |
| Olivia Rose Emporium Limited | Wholesale & retail | 2020 |
| Olro Print Finishers Limited | Manufacturing | 2006 |
| Olti Car Wash Limited | Other services | 2019 |
| Olygrace Ltd | Health & social care | 2025 |
| OM Acubic Cleaning Services Ltd | Administrative & support | 2026 |
| OM Cleaning Ltd | Transport & logistics | 2023 |
| OM Info Solutions Limited | Information & communication | 2016 |
| OM Property Services Limited | Real estate | 2015 |
| OM Roofing & Construction Limited | Construction | 2025 |
| Omania Ltd | Wholesale & retail | 2025 |
| Omar Halal Meats Ltd | Wholesale & retail | 2024 |
| Omar's Projects Ltd | Construction | 2024 |
| Omberai Limited | Health & social care | 2023 |
| Omega Build Construction Ltd | Construction | 2023 |
| Omega Catering Limited | Hospitality | 2025 |
| Omega Electrical Engineering Services Limited | Construction | 2020 |
| Omega Fire & HSE Services Ltd | Professional & scientific | 2020 |
| Omega Recovery Limited | Transport & logistics | 2025 |
| Omega TVN Ltd | Information & communication | 2013 |
| OMG London Ltd | Hospitality | 2025 |
| OMG Prolet Ltd | Real estate | 2025 |
| Omni Concept Marketing Ltd | Professional & scientific | 2025 |
| Omnicart Group Ltd | Wholesale & retail | 2026 |
| Omnidom Limited | Professional & scientific | 2020 |
| Omnixis Technologies Ltd | Information & communication | 2025 |
| Omnyia Limited | Professional & scientific | 2024 |
| OMO Property Rentals Ltd | Real estate | 2026 |
| Ompinteriors Ltd | Construction | 2020 |
| Omran KRD Ltd | Wholesale & retail | 2025 |
| OMS (London) Limited | Wholesale & retail | 2015 |
| OMS Electrical Ltd | Construction | 2021 |
| Omshantiom Ltd Ltd | Real estate | 2024 |
| Omve Construction Ltd | Construction | 2024 |
| ON CUE Media Limited | Information & communication | 2017 |
| ON Demand Workforce Ltd | Administrative & support | 2021 |
| ON One Sports Community CIC | Education | 2021 |
| ON One Sports Management Limited | Administrative & support | 2019 |
| ON Point PM Ltd | Professional & scientific | 2024 |
| ON SET Buses Ltd | Transport & logistics | 2023 |
| ON the Road Events Limited | Hospitality | 2024 |
| ON Time Electrical Ltd | Construction | 2025 |
| ON Time Ltd | Transport & logistics | 2025 |
| ON Tour Global Limited | Wholesale & retail | 2023 |
| ON Your Feet Pods Ltd | Health & social care | 2021 |
| On-Time Shopfront Ltd | Construction | 2014 |
| Onayifood Limited | Hospitality | 2025 |
| Once More Properties Limited | Real estate | 2024 |
| Oncoplastic London Limited | Health & social care | 2015 |
| One 2 One Security Systems Ltd | Administrative & support | 2019 |
| One Accord Partnership Ltd | Information & communication | 2025 |
| One Beauty Ltd | Wholesale & retail | 2006 |
| One Chechi Ltd | Wholesale & retail | 2023 |
| One Click Digital Platform Limited | Information & communication | 2023 |
| One GAS Services Ltd | Extraterritorial | 2017 |