| Offsetk Services LLP | | 2020 |
| OG Foodie Ltd | Hospitality | 2024 |
| Ogbebor Lettings Limited | Real estate | 2023 |
| OH LÀ LÀ YES Limited | Hospitality | 2020 |
| OH My Dosa Limited | Hospitality | 2026 |
| Oh-Buzz Ltd | Wholesale & retail | 2024 |
| Ohass Consultancy Ltd | Information & communication | 2025 |
| OHM Electrical and IT Solutions Ltd | Construction | 2007 |
| OHM GAS Heating and Plumbing Ltd | Other services | 2015 |
| Ohpair Shop Ltd | Wholesale & retail | 2025 |
| Ohsoeasy Limited | Information & communication | 2024 |
| OIL and GAS Certification Services Ltd | Administrative & support | 2008 |
| Oiltech Group for OIL Services & Construction Ltd | Mining & quarrying | 2020 |
| Okaakaa Mmuo Ltd | Construction | 2017 |
| OKI General Trading Ltd | Wholesale & retail | 2023 |
| Oksa Automation Limited | Manufacturing | 2020 |
| Okumagba Invests Ltd | Professional & scientific | 2019 |
| OL Donyo Ltd | Real estate | 2023 |
| Olavo Design Ltd | Arts & recreation | 2018 |
| Old Bakery Tenants Ltd | Households | 2012 |
| Old Windsor Tech Ltd | Professional & scientific | 2026 |
| OLD7SIP Limited | Hospitality | 2024 |
| Oldskool Events Services Ltd | Administrative & support | 2019 |
| Olga Cleaning Ltd | Construction | 2020 |
| OLI Construction Services Limited | Construction | 2019 |
| Olive Community Wembley C.I.C. | Health & social care | 2026 |
| Olive LF Limited | Real estate | 2010 |
| Oliver & Hasani Ltd | Professional & scientific | 2011 |
| Oliver Penguin Ltd | Construction | 2024 |
| Oliverprime Ventures Ltd | Administrative & support | 2026 |
| Olives & Nuts Ltd | Wholesale & retail | 2024 |
| Olives Cuisine Limited | Hospitality | 2020 |
| Olivier Jones Editor Ltd | Information & communication | 2025 |
| Olsi Properties Ltd | Construction | 2022 |
| Olssons Assistance Ltd | Health & social care | 2022 |
| Olumo Rock Enterprises (ORE) Limited | Wholesale & retail | 2013 |
| Olyve Management Ltd | Professional & scientific | 2019 |
| OM Bhakti Shringar Ltd | Wholesale & retail | 2020 |
| OM Events Ltd | Hospitality | 2013 |
| OM Financial Solutions Limited | Administrative & support | 2018 |
| OM Parashakthy Illam PVT Limited | Real estate | 2023 |
| OM SAI Builders Ltd | Construction | 2023 |
| OM SAI Foods Ltd | Hospitality | 2017 |
| OM Shiva Ltd | Real estate | 2026 |
| OME Property Ltd | Real estate | 2023 |
| Omega Astro Ltd | Professional & scientific | 2023 |
| Omega Electricians Ltd | Other services | 2018 |
| Omega PSI Ltd | Manufacturing | 2024 |
| OMJ London Ltd | Wholesale & retail | 2014 |
| Omkar Properties & Developers Ltd | Construction | 2026 |
| Omkarra Private Limited | Wholesale & retail | 2023 |
| Omnimind Ltd | Information & communication | 2019 |
| Omniprime Ltd | Wholesale & retail | 2017 |
| Omnixa Ltd | Wholesale & retail | 2026 |
| Omotoyosi EA Limited | Information & communication | 2023 |
| Omsise Ltd | Information & communication | 2023 |
| Omspice Limited | Hospitality | 2025 |
| ON Cloud Coffee Franchise Ltd | Professional & scientific | 2026 |
| ON Cloud Coffee Holding Ltd | Financial services | 2026 |
| ON Cloud Coffee Ltd | Hospitality | 2026 |
| ON Demand Hospitality Group Ltd | Administrative & support | 2026 |
| ON IT Plumbing & Heating Ltd | Construction | 2026 |
| ON the Rise Music Limited | Arts & recreation | 2011 |
| ON Time Delivery Solutions Limited | Administrative & support | 2015 |
| One Brent CIC | Education | 2026 |
| One Elite Ltd | Transport & logistics | 2019 |
| One Might SAY Studio Ltd | Information & communication | 2024 |
| One Smith House Ltd | Real estate | 2026 |
| One Stop Automotive Centre Ltd | Wholesale & retail | 2024 |
| One Tech Limited | Wholesale & retail | 2023 |
| One-Six.Com Limited | Manufacturing | 1987 |
| ONE2FIVE Technology Limited | Information & communication | 2026 |
| ONE99ESSENTIALS Ltd | Wholesale & retail | 2026 |
| Oneclickspot Ltd | Wholesale & retail | 2025 |
| Onella Herbals Limited | Professional & scientific | 2010 |
| Onesol Sunwarcapitaltrades Ltd | Financial services | 2025 |
| Onetwo Holding Ltd | Real estate | 2019 |
| ONEWAY2VICTORY Limited | Education | 2025 |
| Oniki Limited | Transport & logistics | 2021 |
| Onira Ltd | Extraterritorial | 2025 |
| Onix Build Ltd | Construction | 2020 |
| Online Spects Ltd | Wholesale & retail | 2024 |
| Onlycircle Ltd | Information & communication | 2026 |
| Ontime Accounting Services Ltd | Professional & scientific | 2010 |
| Onyx IT Limited | Information & communication | 2006 |
| Opal GEM (NTH) Limited | Wholesale & retail | 2015 |
| Opex Global Ltd | Professional & scientific | 2025 |
| OPR London Services Ltd | Construction | 2019 |
| Opsmith Labs Ltd | Information & communication | 2026 |
| Optic Shield Security Ltd | Administrative & support | 2025 |
| Optical Glazing Limited | Manufacturing | 2019 |
| Optics AI Ltd | Professional & scientific | 2024 |
| Optiloupe Ltd | Wholesale & retail | 2010 |
| Optima Enablement & Maintenance Limited | Administrative & support | 2006 |
| Optimum Data Solutions Ltd | Administrative & support | 2019 |
| Optionz Limited | Real estate | 2019 |
| Optivance Partners Limited | Information & communication | 2025 |
| Optronix Ltd | Wholesale & retail | 2011 |
| Optuary Ltd | Administrative & support | 2016 |
| Opulent Opulence Ltd | Wholesale & retail | 2024 |