| O&H Construction Ltd | Construction | 2025 |
| O'Tooles Activities Limited | Arts & recreation | 2012 |
| O'Tooles Leisure C.I.C. | Arts & recreation | 2011 |
| O.S.M. Associates Limited | Extraterritorial | 2001 |
| Oak Heath (Send Hill) Residents Management Company Limited | Households | 2021 |
| Oakford Mews Management Company Ltd | Households | 2012 |
| Oakham Park (Crowthorne) Management Company Limited | Households | 2017 |
| Oakhampton Associates Limited | Professional & scientific | 2002 |
| Oakhaven Healthcare Limited | Administrative & support | 2012 |
| Oakland Farm (Residents Management Company) Ltd | Households | 2023 |
| Oakland Grove (Chiddingfold) Management Company Limited | Households | 2025 |
| Oakleigh Close Limited | Households | 2018 |
| Oakmere Estates Group Ltd | Real estate | 2026 |
| Oakpod Ltd | Real estate | 2016 |
| Oakwood-Ps Limited | Construction | 2011 |
| Oasis Worlds Title Limited | Professional & scientific | 2013 |
| Obsidian Healthcare Recruitment Limited | Administrative & support | 2020 |
| Occassion Wedding Supplies Ltd | Other services | 2022 |
| OCD Logistics Ltd | Wholesale & retail | 2026 |
| Oceanland Logistics Limited | Administrative & support | 2006 |
| Oceanside Solutions Limited | Transport & logistics | 2010 |
| Ochre Knitwear Limited | Wholesale & retail | 2004 |
| Ockendon Tackle Supplies Limited | Wholesale & retail | 2019 |
| Ockley Plumbing Limited | Construction | 1968 |
| Octagon Sweets Limited | Wholesale & retail | 2019 |
| OFF the Shelf Recordings Ltd | Manufacturing | 2019 |
| Offerofservice (OOS) Limited | Information & communication | 2017 |
| Offshore Structural Engineering Consultants Limited | Professional & scientific | 2013 |
| Ohlson Consultancy Service Ltd | Professional & scientific | 2021 |
| OI FOY Limited | Financial services | 2023 |
| OI OI Saveloy Ltd | Information & communication | 2022 |
| OIC Limited | Wholesale & retail | 2023 |
| OJ Fresh Limited | Hospitality | 2000 |
| OJH Solutions Ltd | Wholesale & retail | 2025 |
| Ojuola Limited | Health & social care | 2014 |
| OKI Bazaar Ltd | Wholesale & retail | 2025 |
| Okvidian Limited | Construction | 2024 |
| Olandata Limited | Information & communication | 1984 |
| Old Avenue House Residents Association Limited | Households | 1992 |
| Old Brew House Woking Management Ltd | Households | 2019 |
| Old Dean Kitchens Ltd | Hospitality | 2025 |
| Old Hamsey Lakes Residents Management Company Ltd | Households | 2020 |
| Old Royalists' Association in the UK Ltd | Other services | 2005 |
| Oldfield & Company Limited | Professional & scientific | 2012 |
| Oldfields Management Company Limited | Households | 2007 |
| Oldriver Limited | Construction | 2024 |
| Olivander Investments Limited | Construction | 2021 |
| Olive Ridley Ltd | Information & communication | 2018 |
| Olivia Brooke Floral Design Ltd | Administrative & support | 2017 |
| Olivia Samuel Limited | Professional & scientific | 2024 |
| Ollomani Investments Ltd | Real estate | 2023 |
| Olympusindustial Ltd | Wholesale & retail | 2026 |
| OM SRI Sairam (PVT) Ltd | Hospitality | 2024 |
| OM Tech Holdings Limited | Information & communication | 2018 |
| Omega Paving & Artificial Grass Ltd | Administrative & support | 2017 |
| Omkar Holdings Limited | Professional & scientific | 2026 |
| Omniavatar.Net Limited | Professional & scientific | 2019 |
| Omniter Limited | Professional & scientific | 2020 |
| Omparu Superstore Ltd | Wholesale & retail | 2016 |
| Onbeam Investments Limited | Construction | 2006 |
| One Call Crew Ltd | Professional & scientific | 2025 |
| One Circle Consulting Ltd | Information & communication | 2023 |
| One Eight Real Estate Limited | Real estate | 2023 |
| One Generation Recruitment Limited | Administrative & support | 2025 |
| One Plan, One PAN Ltd | Health & social care | 2022 |
| One Point Capital SPV Ltd | Real estate | 2021 |
| One Services Ltd | Construction | 2008 |
| One Stop Childcare Training Ltd | Education | 2020 |
| One Vision Pro Limited | Information & communication | 2025 |
| Onid Limited | Information & communication | 1994 |
| Onlymans Ltd | Professional & scientific | 2025 |
| Onpoint I.T.Services Limited | Information & communication | 2010 |
| Ontel Ltd | Information & communication | 1999 |
| Opalstar Limited | Real estate | 2002 |
| Open Perspective Ltd | Professional & scientific | 2026 |
| Open Road Campers Ltd | Wholesale & retail | 2021 |
| Openside Investments Limited | Real estate | 2020 |
| Opensolve Ltd | Information & communication | 1996 |
| Opentalent.Com Holdings Limited | Administrative & support | 2024 |
| Operatic Productions Limited | Arts & recreation | 2009 |
| Ophir Occupational Therapy and Specialist Cleaning Services Ltd | Administrative & support | 2025 |
| OPS Partner Ltd | Administrative & support | 2025 |
| Optasense Holdings Limited | Professional & scientific | 2010 |
| Optasense Limited | Professional & scientific | 2008 |
| Optimal Climate Ltd. | Construction | 2016 |
| Optimize AI Ltd | Information & communication | 2025 |
| Optimum Performance Clinic Limited | Health & social care | 2011 |
| Optimum Television Ltd | Administrative & support | 2005 |
| Optiplexa Ltd | Information & communication | 2026 |
| Optplan Consulting Ltd | Information & communication | 2010 |
| ORA Studio (Pilates & Wellness) Limited | Other services | 2025 |
| Orada Limited | Professional & scientific | 2014 |
| Orana Properties Limited | Real estate | 2023 |
| Orange Earth Construction Ltd | Construction | 2015 |
| Orchadia Ltd | Wholesale & retail | 2013 |
| Orchard Car Sales Ltd | Wholesale & retail | 2011 |
| Orchard Rise Agriculture Limited | Agriculture & fishing | 2017 |
| ORG Engineering Ltd | Professional & scientific | 2022 |
| Oriental RUG Spa Limited | Administrative & support | 2022 |
| Original Doughnuts International Limited | Financial services | 2025 |