| OK Shop (Rossington) Ltd | Wholesale & retail | 2025 |
| OK Shop Limited | Wholesale & retail | 2023 |
| Ok-Yeah Bakery & Snacks Ltd | Extraterritorial | 2024 |
| Okdc Ltd | Transport & logistics | 2020 |
| Okeanya Ltd | Real estate | 2025 |
| Okey Logistic Ltd | Construction | 2024 |
| Okuns Cutz Ltd | Other services | 2025 |
| Okyanus Ltd | Hospitality | 2025 |
| Olafs Bouncy Castle Hire Doncaster Ltd | Arts & recreation | 2023 |
| Olaizola Limited | Health & social care | 2018 |
| Olam Solutions Ltd | Real estate | 2025 |
| Olawa Bakery Online Ltd | Wholesale & retail | 2023 |
| Old Boatyard Apartments Thorne Limited | Households | 2004 |
| Old Building Ltd | Real estate | 2021 |
| Old Forge Engine Centre Ltd | Wholesale & retail | 2015 |
| Old MAN Staveleys Coffee Co Ltd | Wholesale & retail | 2024 |
| Old Sycamore Place Apartments Limited | Households | 2019 |
| Old Sycamore Place Managment Company Ltd | Households | 2018 |
| Old Technology Ltd | Information & communication | 2023 |
| Old Timer Mining Limited | Extraterritorial | 2021 |
| Olegexpress Ltd | Wholesale & retail | 2021 |
| Olegsexpress Ltd | Transport & logistics | 2020 |
| Oleo Environmental Limited | Water & waste | 2020 |
| Oleo Recycling Limited | Water & waste | 2020 |
| OLI Rock Management Limited | Wholesale & retail | 2017 |
| Oli&Mary Auto Ltd | Wholesale & retail | 2021 |
| Olive Lane Food Limited | Hospitality | 2025 |
| Oliver Anna Limited | Administrative & support | 2017 |
| Oliver Brian Productions Ltd | Information & communication | 2016 |
| Oliver HMO & Building Limited | Construction | 2013 |
| Oliver Law Security Ltd | Administrative & support | 2011 |
| Oliver SJ Barber Shop Ltd | Other services | 2025 |
| Oliver Smith Limited | Health & social care | 2023 |
| Oliver Stafford Studio Limited | Professional & scientific | 2025 |
| Oliver's Traditional Barbershop Ltd | Other services | 2018 |
| Olivia & Will Realty Limited | Real estate | 2022 |
| Olivia & Will Wealth Management Limited | Real estate | 2024 |
| Olivia MAY Transport Limited | Transport & logistics | 2025 |
| Olivia Rose Commercial Limited | Real estate | 2023 |
| Olivianacars Ltd | Wholesale & retail | 2025 |
| Ollie & Black Limited | Professional & scientific | 2015 |
| Olly & Poppy Limited | Wholesale & retail | 2017 |
| Ollys Place Restuarant Ltd | Hospitality | 2025 |
| OLS Connect Limited | Information & communication | 2025 |
| OLS Hive Limited | Real estate | 2025 |
| Olsen RJ Ltd | Transport & logistics | 2026 |
| Olszewski Solutions Ltd | Administrative & support | 2025 |
| Oltean Trading Ltd | Wholesale & retail | 2020 |
| Oltenia Transport Logistics Limited | Transport & logistics | 2025 |
| Olusheye and Sons Limited | Health & social care | 2018 |
| Olympia Court Limited | Real estate | 2013 |
| Olympus Joinery Specialist Ltd | Other services | 2017 |
| Olzak N.D.T Inspections Ltd | Professional & scientific | 2019 |
| Omar Car Sale Limited | Wholesale & retail | 2025 |
| Omar+ Limited | Information & communication | 2025 |
| Omega Bidco Limited | Professional & scientific | 2008 |
| Omega Business Services Limited | Real estate | 2004 |
| Omega International Group Limited | Professional & scientific | 1995 |
| Omega Kitchens Limited | Professional & scientific | 2000 |
| Omega PLC | Manufacturing | 1992 |
| Omega Topco Limited | Manufacturing | 2009 |
| Omegachem Limited | Manufacturing | 2011 |
| Omni Eco Limited | Construction | 2025 |
| Omni House Management Company Limited | Extraterritorial | 2008 |
| Omnia Go Ltd | Information & communication | 2025 |
| Omnia Mutantor Ltd | Wholesale & retail | 2016 |
| Omnia South Ltd | Wholesale & retail | 2025 |
| Omnico Automotive Ltd Ltd | Wholesale & retail | 2025 |
| Omnious Transport Limited | Transport & logistics | 2026 |
| OMV Logistic Ltd | Transport & logistics | 2020 |
| ON the Ball Cleaning Ltd | Administrative & support | 2025 |
| ON the T CIC | Arts & recreation | 2025 |
| ON the Terrace GD Ltd | Wholesale & retail | 2026 |
| ON Track Properties Limited | Construction | 2017 |
| One Call Build Limited | Construction | 2020 |
| One Call Claims Limited | Administrative & support | 2003 |
| One Call Estates Limited | Real estate | 2003 |
| One Call Group Companies Limited | Financial services | 2017 |
| One Call Insurance Services Limited | Financial services | 2003 |
| One Call Mortgage Hub Ltd | Financial services | 2013 |
| One Call Technologies Limited | Information & communication | 2016 |
| One Coaching Ltd | Arts & recreation | 2023 |
| One Deal Engineering Consultants Ltd | Extraterritorial | 2015 |
| One Fine Day Studios Ltd | Wholesale & retail | 2025 |
| One GUY Limited | Transport & logistics | 2018 |
| One Hope Street Ltd | Real estate | 2015 |
| One Million Commercial Ltd | Financial services | 2025 |
| One Shared Home Ltd | Wholesale & retail | 2024 |
| One Stop Advice Service Limited | Other services | 2013 |
| One Stop Scaffolding & Netting Services Limited | Construction | 2009 |
| Onerack Installations Limited | Construction | 2025 |
| Onesite (Laser) Limited | Manufacturing | 2008 |
| Oneuk Ltd | Professional & scientific | 2015 |
| Onevitality Ltd | Manufacturing | 2021 |
| Oneway Marketing Global Ltd | Professional & scientific | 2025 |
| Only Dentz Ltd | Wholesale & retail | 2025 |
| ONM Construction Group Ltd | Construction | 2025 |
| ONM Kitchens Ltd | Manufacturing | 2023 |
| Onside Events Ltd | Administrative & support | 2016 |
| Onsite Driveways Limited | Wholesale & retail | 2015 |