| Octopus Impact Ltd | Professional & scientific | 2025 |
| Octopus Property Management Ltd | Real estate | 2020 |
| Oddform Games Ltd | Information & communication | 2026 |
| Odeseay Limited | Real estate | 2024 |
| Odie Solutions Ltd | Professional & scientific | 2025 |
| Odyssey Bath Ltd | Administrative & support | 2017 |
| Odyssey People Development Limited | Professional & scientific | 2021 |
| OFF the Rock Ltd | Manufacturing | 2022 |
| Office Works Ltd | Real estate | 2016 |
| Official Events Ltd | Administrative & support | 2022 |
| Offshore Solutions Limited | Professional & scientific | 2000 |
| Offshore Survey & Engineering Ltd | Construction | 2012 |
| Offside Culture UK Limited | Wholesale & retail | 2025 |
| OHM Protocol CIC | Information & communication | 2026 |
| Ohvert Ltd | Professional & scientific | 2019 |
| Oikonomiki Limited | Professional & scientific | 2021 |
| Oikos Chartered Architects Limited | Professional & scientific | 2006 |
| OJ Electronics Limited | Wholesale & retail | 1988 |
| OKS Property LLP | | 2010 |
| Okuva Ltd | Manufacturing | 2021 |
| Old Apple Property Limited | Real estate | 2010 |
| Old Crown (Bath) Limited | Hospitality | 2014 |
| Old Pottery (Horton) Ltd | Construction | 2020 |
| Old Quay House Hotel Limited | Financial services | 2015 |
| Oldfield Book Keeping Services Ltd | Administrative & support | 2022 |
| Oldfield Park Management Limited | Households | 2010 |
| Oldfield RFC Ltd | Arts & recreation | 2021 |
| Oldfield School | Education | 2011 |
| Olds School Restoration Ltd | Construction | 2024 |
| Oldwood Pits Ltd | Agriculture & fishing | 2025 |
| Olea Mediterranean Limited | Hospitality | 2020 |
| Olive Consulting Group Ltd | Professional & scientific | 2025 |
| Olive Tree Studios (Bath) Ltd | Manufacturing | 2026 |
| Oliver Financial Planning Ltd | Financial services | 2021 |
| Oliver Hazael Limited | Construction | 2017 |
| Oliver Joseph Limited | Other services | 2010 |
| Olivia Connelly Limited | Arts & recreation | 2009 |
| Olivia Grace Properties Limited | Professional & scientific | 2023 |
| Oliwia Property Ltd | Real estate | 2025 |
| Olja Limited | Administrative & support | 2018 |
| OM Socials Ltd | Professional & scientific | 2025 |
| Omadikos Ltd | Professional & scientific | 2026 |
| OMB Properties Ltd | Real estate | 2022 |
| OMH Ltd | Hospitality | 2006 |
| Omid Transport Ltd | Transport & logistics | 2026 |
| OMM & Khushi Enterprises Limited | Wholesale & retail | 2025 |
| OMM & Khushi Hospitality Ltd | Hospitality | 2021 |
| Omni Business Ltd. | Extraterritorial | 2008 |
| Omnia Corporation Ltd | Information & communication | 2016 |
| Omnia Online Limited | Professional & scientific | 2015 |
| Omnialegal Executor and Trustees Limited | Professional & scientific | 2011 |
| Omnialegal Limited | Professional & scientific | 2009 |
| Omnidex Limited | Professional & scientific | 2019 |
| OMS Property Limited | Real estate | 2023 |
| ON a Cloud Limited | Information & communication | 2016 |
| Onconn Limited | Information & communication | 2021 |
| One Beaufort (Bath) Limited | Households | 2024 |
| One Bilbury Lane Limited | Households | 2020 |
| One Day Clothing Company Ltd | Wholesale & retail | 2025 |
| One Devonshire Place Management Company Limited | Extraterritorial | 1988 |
| One KR Ltd | Wholesale & retail | 2021 |
| One Manvers Street Limited | Households | 2008 |
| One More Time Ltd | Professional & scientific | 2025 |
| One Raby Place Ltd | Real estate | 2022 |
| One Sunny Day Ltd | Information & communication | 2025 |
| One Track Pony Ltd | Real estate | 2019 |
| One Tree Software Limited | Information & communication | 2012 |
| One Twenty Pictures Ltd | Professional & scientific | 2005 |
| Onebetweensj Limited | Professional & scientific | 2026 |
| Onelog Ltd | Information & communication | 2026 |
| Onemeal Group Ltd | Manufacturing | 2025 |
| Onesmartsolutions Limited | Professional & scientific | 2004 |
| Onesub Ltd | Information & communication | 2019 |
| Online Data Storage UK Limited | Real estate | 2014 |
| Online Media Consulting Limited | Information & communication | 2015 |
| Onlineservicescompanylh Ltd | Information & communication | 2026 |
| Only Experience Counts Limited | Extraterritorial | 2017 |
| Only FOD Limited | Wholesale & retail | 2023 |
| Only Pans Limited | Hospitality | 2026 |
| Oort IP Limited | Professional & scientific | 2012 |
| Ootle Ltd | Professional & scientific | 2025 |
| Opal Print (Bath) Limited | Administrative & support | 2011 |
| Opdc Limited | Other services | 2001 |
| Open Door Renewables Ltd. | Construction | 2011 |
| Open Inform Limited | Professional & scientific | 2022 |
| Open Space Network Ltd | Professional & scientific | 2020 |
| Openings (Bath) Limited | Health & social care | 1998 |
| Operating Talent Partners Ltd | Administrative & support | 2023 |
| Ophia Ltd | Information & communication | 2022 |
| Opilio Limited | Professional & scientific | 2021 |
| Opium Bars Ltd | Hospitality | 2009 |
| Oppen Limited | Construction | 2010 |
| Opspace Projects Ltd | Construction | 2010 |
| Optect Ltd | Information & communication | 2017 |
| Optibayes LAB Ltd | Wholesale & retail | 2025 |
| Optidek Ltd | Manufacturing | 2021 |
| Optimak Limited | Information & communication | 2021 |
| Optimal Database Limited | Information & communication | 2011 |
| Optimal UK Property & Investment Ltd | Real estate | 2023 |
| Optimax Solutions Limited | Administrative & support | 2022 |