| Oakstone Home Improvements Ltd | Construction | 2026 |
| Oaktree Builders Cheltenham Limited | Construction | 2004 |
| Oaktree Nurseries Limited | Real estate | 1996 |
| Oaktree Renovations Ltd | Construction | 2013 |
| Oakview Estates Ltd | Real estate | 2020 |
| Oakview Property Management Ltd | Households | 2022 |
| Oakway Wealth Management Limited | Financial services | 2015 |
| Oakwell (118) Ltd | Construction | 2026 |
| Oakwell Construction & Development Ltd | Construction | 2026 |
| Oakwood Builders (Cheltenham) Limited | Construction | 2003 |
| Oakwood ED Ltd | Education | 2026 |
| Oakwoods Bespoke Limited | Construction | 2017 |
| Oates and Oates Limited | Information & communication | 2007 |
| Oath Limited | Health & social care | 2020 |
| Oathouse Limited | Professional & scientific | 2004 |
| OB Films Ltd | Information & communication | 2005 |
| OBA Home Limited | Wholesale & retail | 2022 |
| Obar Property Limited | Real estate | 2022 |
| Obee Language Consultants Ltd | Education | 2013 |
| Obel Properties Ltd | Real estate | 2023 |
| Obelix Systems Limited | Manufacturing | 2020 |
| Objective Answers Limited | Information & communication | 1998 |
| Obsidian Home and Garden Limited | Wholesale & retail | 2020 |
| OC Advisory Limited | Professional & scientific | 2020 |
| Occultus Ltd | Professional & scientific | 2012 |
| Occupational Performance Group Ltd | Health & social care | 2026 |
| Ocean Dental Limited | Health & social care | 2007 |
| Oceans Hotel Representation Limited | Hospitality | 2020 |
| Ocere Limited | Professional & scientific | 2009 |
| Ocho Ocho Asian Foods Ltd | Hospitality | 2021 |
| Ocho Ocho Asian Goods Evesham Limited | Wholesale & retail | 2023 |
| Octo Construction Equipment Ltd | Wholesale & retail | 2024 |
| Oculoplastics Centre UK Ltd | Health & social care | 2020 |
| Oculus Wealth Management (Cheltenham) Limited | Financial services | 2018 |
| Odd-Jobs Group Ltd | Information & communication | 2026 |
| OFF Grid Renewables Ltd | Wholesale & retail | 2024 |
| Off-Piste Limited | Extraterritorial | 2006 |
| Offbeat Interiors Limited | Arts & recreation | 2014 |
| Offgridsolarsystems Ltd | Construction | 2021 |
| Office Holidays Ltd. | Information & communication | 2014 |
| Office of Computer Programs Ltd | Information & communication | 2022 |
| Officeworx Ltd | Manufacturing | 1997 |
| Offmore Property Limited | Real estate | 2018 |
| Ogdens Drainage Services Ltd | Construction | 2015 |
| OGM Property Group Ltd | Financial services | 2024 |
| OH My Music Limited | Arts & recreation | 2022 |
| OH SO Delightful Limited | Wholesale & retail | 2024 |
| OHL Subsidiary Limited | Extraterritorial | 2018 |
| Ohta Music Ltd | Arts & recreation | 2024 |
| OI Creative Ltd | Information & communication | 2015 |
| OI Digital Ltd | Information & communication | 1999 |
| OI Limited | Extraterritorial | 2007 |
| Oilwell Garage Ltd | Wholesale & retail | 2022 |
| OJ Polo Ponies Limited | Agriculture & fishing | 2021 |
| OJT Technologies Limited | Information & communication | 2026 |
| OJW and Co Limited | Information & communication | 2019 |
| Okeke Ventures and Associates Limited | Real estate | 2019 |
| OKM Events Ltd | Professional & scientific | 2017 |
| OKO by Marlena Ltd | Wholesale & retail | 2025 |
| Old Abbey Properties and Investment Limited | Real estate | 2025 |
| Old Chapel Communications Limited | Professional & scientific | 2011 |
| Old Faithful Collective Ltd | Arts & recreation | 2023 |
| Old Farm Solar Limited | Energy | 2022 |
| Old Homes Propco 1 Ltd | Construction | 2025 |
| Old Homes Propco 2 Ltd | Construction | 2025 |
| Old Homes Propco 3 Ltd | Construction | 2025 |
| Old Homes Propco 4 Ltd | Construction | 2025 |
| Old Homes Propco 5 Ltd | Construction | 2025 |
| Old Liberal Club Ltd | Real estate | 2024 |
| Old Library Mews Management Company Limited | Administrative & support | 2016 |
| Old Lodge Court Management Company Limited | Professional & scientific | 2000 |
| Old Rock Equestrian Limited | Agriculture & fishing | 2021 |
| Old VAT House Management Company Limited(The) | Households | 1986 |
| Oldcroft Properties Ltd | Construction | 2023 |
| Oldfield Crescent Management Company Limited | Households | 2006 |
| Olea Craft Limited | Wholesale & retail | 2026 |
| Olive & Barr Elkstone Limited | Wholesale & retail | 2023 |
| Olive Clothing Limited | Wholesale & retail | 2013 |
| Olive Hill Construction Limited | Construction | 2021 |
| Olivelle Holdings Limited | Health & social care | 2009 |
| Oliver & Oscar Ltd | Other services | 2023 |
| Olivia Ocean Ltd | Other services | 2019 |
| Olney Dental Care Limited | Health & social care | 2022 |
| Oltomo Limited | Information & communication | 2021 |
| Olympus Safety Limited | Extraterritorial | 1990 |
| Omat Limited | Wholesale & retail | 2005 |
| Omcontracting Ltd | Construction | 2024 |
| Omega Air Holidays Limited | Transport & logistics | 2003 |
| Omega Coach Company Limited | Transport & logistics | 1996 |
| Omega Digital Limited | Administrative & support | 2002 |
| Omega Holidays Group Limited | Professional & scientific | 2009 |
| Omega Holidays Limited | Administrative & support | 1987 |
| Omega Structures Ltd | Other services | 2005 |
| OMG Installations Limited | Construction | 2010 |
| Omicron Adhesive Materials Ltd | Professional & scientific | 2012 |
| Omni Consultancy Services Ltd | Information & communication | 2018 |
| Omniaqua Ltd | Professional & scientific | 2025 |
| Omnihold Ltd | Financial services | 2024 |
| Omor Investment Ltd | Hospitality | 2025 |
| Omor Properties Ltd | Real estate | 2025 |