| Omer Holding Limited | Financial services | 2024 |
| OML Consulting Engineers Ltd | Professional & scientific | 2023 |
| Omnibell Limited | Manufacturing | 2020 |
| Omnicon UK Limited | Other services | 2023 |
| Omnicron 12 Limited | Real estate | 2014 |
| Omnify Technologies Limited | Information & communication | 2025 |
| ON Track Coffee Ltd | Hospitality | 2022 |
| Onboarding Group Limited | Education | 2019 |
| One Albert Terrace Limited | Real estate | 2023 |
| One Barbers Limited | Other services | 2024 |
| One EX Consulting Ltd | Professional & scientific | 2021 |
| One Life PD Limited | Professional & scientific | 2026 |
| One SD Limited | Financial services | 2023 |
| One Small Step Day Nursery Limited | Education | 2015 |
| One Stop Tyres Wakefield Ltd | Wholesale & retail | 2026 |
| One Stop Wolverhampton Ltd | Wholesale & retail | 2024 |
| One to One Development Trust | Information & communication | 2004 |
| One Ummah Community CIC | Education | 2022 |
| One Unity Ltd | Hospitality | 2015 |
| One Vision Construction Ltd | Water & waste | 2019 |
| Onebelt Group Ltd | Wholesale & retail | 2014 |
| Onetek Security Limited | Administrative & support | 2013 |
| Ongoing Developments Limited | Professional & scientific | 2005 |
| Online and Direct Group Ltd | Wholesale & retail | 2022 |
| Online Solution INT Limited | Administrative & support | 2009 |
| Online Trade Marketing Ltd. | Professional & scientific | 2014 |
| Only YOU Exclusive Ltd | Wholesale & retail | 2024 |
| Ontario Property Ltd | Real estate | 2015 |
| Onyx Solutions Limited | Professional & scientific | 2005 |
| Opal BID Consultants Ltd | Professional & scientific | 2025 |
| Opal Blush Studio Limited | Manufacturing | 2025 |
| Opal Recruitment Consultants Ltd | Administrative & support | 2022 |
| Opemsuo Nananom Ltd | Education | 2026 |
| Open Arms Homes for Women | Hospitality | 2019 |
| Open Communications UK Limited | Administrative & support | 2008 |
| Open Draft Limited | Hospitality | 2015 |
| Open Mode Limited | Hospitality | 2008 |
| Operth Ltd | Professional & scientific | 2021 |
| Oporto Properties Ltd | Real estate | 2021 |
| Optie Ltd | Administrative & support | 2024 |
| Optik AM Rotenbuehl Limited | Administrative & support | 2005 |
| Optilife 24/7 Care Services Limited | Health & social care | 2022 |
| Optima Measurement and Analytics Ltd | Mining & quarrying | 2018 |
| Optimal Outsourcing Ltd | Mining & quarrying | 2008 |
| Optimise Marketplace Limited | Wholesale & retail | 2025 |
| Optimum Exposure Limited | Information & communication | 2009 |
| Optimum Grips Limited | Arts & recreation | 2012 |
| Optimum Laser Ltd | Manufacturing | 2025 |
| Optimum Racing Ltd | Wholesale & retail | 2015 |
| Optio Resourcing Ltd | Administrative & support | 2024 |
| Orange Fire Protection Group Ltd | Construction | 2014 |
| Orange Stone Limited | Information & communication | 1998 |
| Oranmore Holdings Limited | Real estate | 2015 |
| Orbital Group International Limited | Administrative & support | 2007 |
| Orchard Croft Pharma Ltd | Wholesale & retail | 2026 |
| Orchard Physiotherapy Centre Limited | Health & social care | 2012 |
| Orchard Recruitment Solutions Limited | Administrative & support | 2007 |
| Ordys Transport Ltd | Transport & logistics | 2019 |
| Orgidea Limited | Administrative & support | 2006 |
| Origin Blue Ltd | Real estate | 2025 |
| Orion Express Logistics Ltd | Transport & logistics | 2025 |
| Orion GLE Ltd | Information & communication | 2025 |
| Orion Land Limited | Construction | 2000 |
| Oritsu MA Ltd | Arts & recreation | 2021 |
| ORM Consultancy Ltd | Professional & scientific | 2025 |
| Orzelek Foods Limited | Wholesale & retail | 2018 |
| Orzelek International Foods Limited | Wholesale & retail | 2022 |
| Orzjc Reloaded Ltd | Health & social care | 2022 |
| Oscar Lettings Ltd | Real estate | 2025 |
| Osceola Limited | Real estate | 2018 |
| OSI (2021) Limited | Wholesale & retail | 2021 |
| Osiligi Ltd | Health & social care | 2025 |
| Osler Properties Ltd | Real estate | 2025 |
| Oslo Agency Ltd | Professional & scientific | 2015 |
| Osprey Process Engineering Limited | Professional & scientific | 2011 |
| Ossett Childcare & Pre-School Limited | Health & social care | 2017 |
| Ossett Town Juniors FC Ltd | Arts & recreation | 2018 |
| Ossett Town Juniors Ltd | Arts & recreation | 2019 |
| OT Trade International Ltd | Information & communication | 2023 |
| Otlon Services Ltd | Professional & scientific | 2023 |
| OTW Properties Ltd | Real estate | 2022 |
| Oulton Chapel Management Company Ltd. | Households | 2010 |
| OUT OUT Projects LLP | | 2024 |
| Outdoor World Direct Limited | Real estate | 2015 |
| Outside of the Box Marketing Ltd | Professional & scientific | 2014 |
| Outwood Express Ltd | Wholesale & retail | 2022 |
| Outwood Grange Academies Trust | Education | 2009 |
| Outwood Grange Services Limited | Education | 2011 |
| Outwood Interiors Ltd | Construction | 2015 |
| Outwood Kitchen Ltd | Hospitality | 2026 |
| Outwood Supershine Ltd | Other services | 2022 |
| Ovatone Ltd | Information & communication | 2026 |
| Oven Door (Wakefield) Ltd | Wholesale & retail | 2018 |
| Over the Balloon Ltd | Wholesale & retail | 2023 |
| Over the NET - Wakefield Limited | Arts & recreation | 2026 |
| Overdrive MOT Stop Ltd | Professional & scientific | 2022 |
| Overdrive One Stop Service Ltd | Wholesale & retail | 2022 |
| Overdrive Wakefield Ltd | Wholesale & retail | 2015 |
| Overflow Homes Ltd | Real estate | 2021 |
| Overflow Smart Vending Ltd | Wholesale & retail | 2025 |