| Office IS Holdings Ltd | Financial services | 2024 |
| Office IS Ltd | Wholesale & retail | 2008 |
| Office Owls Recruitment Limited | Other services | 2019 |
| Office Pathfinders Ltd | Real estate | 2018 |
| Office Tech Document Solutions Ltd | Information & communication | 2026 |
| Office Tech Software Ltd | Extraterritorial | 2024 |
| Office Tech Suite Holdings Ltd | Financial services | 2025 |
| Office Tech Suite Ltd | Information & communication | 2019 |
| Office Zombies Limited | Extraterritorial | 2009 |
| Officeserve Technologies Ltd | Hospitality | 2011 |
| Officiating Services Limited | Arts & recreation | 2019 |
| Officium Private Wealth Ltd | Professional & scientific | 2021 |
| Offnic 3THIRTEEN Venture Angels Limited | Financial services | 2023 |
| Offona Ltd | Information & communication | 2013 |
| Offpiste Leadership Ltd | Information & communication | 2026 |
| Offshore Consult Limited | Professional & scientific | 2019 |
| Offshore Inspection Lifting Consultancy Ltd | Extraterritorial | 2022 |
| Offshore Marine Equipment Limited | Administrative & support | 2018 |
| Offshore Marine Management Holdings Limited | Professional & scientific | 2012 |
| Offshore Marine People and Academy Limited | Education | 2009 |
| Offspring Films Limited | Information & communication | 2014 |
| Offtech Projects & Technologies Ltd | Professional & scientific | 2011 |
| Ofso Limited | Professional & scientific | 2016 |
| OG Real Estate Ltd | Real estate | 2024 |
| OGD Investments Ltd | Real estate | 2023 |
| Ogems Limited | Manufacturing | 2024 |
| Oggadoon Limited | Administrative & support | 2008 |
| Ogie Ltd | Construction | 2025 |
| OGL Curve Holdings Ltd | Financial services | 2025 |
| Ogl&P Limited | Real estate | 2023 |
| Ogmore Power Limited | Energy | 2014 |
| Ognisko Sport & Entertainment Ltd | Arts & recreation | 2020 |
| OGO Roofing &Cladding Limited | Construction | 2026 |
| OGT Clinical Ltd | Professional & scientific | 2017 |
| Oguzhan Limited | Wholesale & retail | 2008 |
| OH Bees City Ltd | Information & communication | 2024 |
| OH Calcutta BRS Ltd | Hospitality | 2015 |
| OH My Goddess Ltd | Wholesale & retail | 2013 |
| OH My! PIE Co Ltd | Hospitality | 2026 |
| OH WOW Gifts Limited | Wholesale & retail | 2021 |
| Ohana Designs Limited | Wholesale & retail | 2016 |
| Ohana Property Group Ltd | Real estate | 2025 |
| Ohana Studio Ltd | Information & communication | 2020 |
| Ohbeone Limited | Professional & scientific | 2025 |
| OHC Services Limited | Health & social care | 2016 |
| Ohdm Performance Ltd | Administrative & support | 2026 |
| Ohem Music Ltd | Information & communication | 2022 |
| Ohfs Health Foods Ltd | Wholesale & retail | 2009 |
| Ohinemuri Media Limited | Arts & recreation | 2012 |
| Ohlala Bakery Ltd | Hospitality | 2025 |
| OI Services Ltd | Administrative & support | 2022 |
| OIC UK, LLP | | 2022 |
| Oiexchange Ltd | Hospitality | 2021 |
| Oiik Ltd | Other services | 2025 |
| OIL GAS and Marine Limited | Construction | 2015 |
| OIL Inspections Limited | Manufacturing | 1981 |
| OIL Well Tool Design and Compliance Limited | Manufacturing | 2012 |
| Oily's Engineering Services Ltd | Wholesale & retail | 2021 |
| OJ Actions Limited | Information & communication | 2013 |
| OJ Digital Solutions Limited | Information & communication | 2017 |
| OJ Estates Limited | Real estate | 2025 |
| OJ Mortgages Ltd | Financial services | 2023 |
| Ojal Bikes LP | | 2014 |
| OJB Property Solutions Ltd | Construction | 2023 |
| Ojfpitt Consulting Limited | Information & communication | 2016 |
| OJR Duomi Ltd | Hospitality | 2026 |
| Ojwa Consulting Ltd | Professional & scientific | 2024 |
| OK Consultancy (UK) Limited | Information & communication | 2005 |
| Okab Solar Limited | Energy | 2023 |
| Okasa Healthcare Ltd | Health & social care | 2019 |
| Okeford House Management Limited | Households | 1997 |
| Okere Consultant Ltd | Information & communication | 2016 |
| OKO Solutions Ltd | Construction | 2018 |
| Okrad Ltd | Other services | 2020 |
| Oksara LP | | 2013 |
| OKU Studio Limited | Professional & scientific | 2016 |
| Okulo Ltd | Professional & scientific | 2018 |
| OL Property Ltd | Real estate | 2021 |
| OLA Studio Limited | Manufacturing | 2019 |
| Olaf Site Management Limited | Construction | 2016 |
| Olagunjupmc Limited | Real estate | 2020 |
| Olaj Ltd | Construction | 2018 |
| Olakunle S OJO Ltd | Health & social care | 2016 |
| Olas Associates Limited | Professional & scientific | 2025 |
| Olaus ROE Limited | Information & communication | 2007 |
| Olclean Ltd | Administrative & support | 2024 |
| Olcompany Ltd | Other services | 2024 |
| Old Brewery Auctions Ltd | Wholesale & retail | 2024 |
| Old Bristolians' Sports Club | Arts & recreation | 2022 |
| Old City Studio Limited | Information & communication | 2024 |
| Old City Trading Limited | Hospitality | 2014 |
| Old Coach Drive Residents Limited | Households | 1988 |
| Old Coombe House Limited | Real estate | 2024 |
| Old Exchange Building Management Company Limited | Households | 2021 |
| Old Farm Court Management (Elberton) Limited | Households | 1994 |
| Old Farm Limited | Hospitality | 2013 |
| Old Forge Mews Management Limited | Households | 2012 |
| Old FOX Ltd | Real estate | 2019 |
| Old Hall Investment Company Limited | Administrative & support | 2007 |
| Old Market Barber Ltd | Other services | 2021 |