| Omnicorp Properties Ltd | Construction | 2025 |
| Omnilert SLS Ltd | Manufacturing | 2025 |
| Omnix Ventures Ltd | Wholesale & retail | 2026 |
| OMR Group Holdings Ltd | Financial services | 2026 |
| ON Grid Site Engineering Limited | Professional & scientific | 2004 |
| ON the Move Removals (Huddersfield) Ltd | Transport & logistics | 2015 |
| ON the Verge Ltd | Real estate | 2022 |
| Oncall GP Limited | Health & social care | 2012 |
| Oncanova Ltd | Professional & scientific | 2025 |
| Ondeen Limited | Wholesale & retail | 2023 |
| One 17 ED (Education) Limited | Arts & recreation | 2000 |
| One 17 PM (Project Management) Limited | Construction | 1988 |
| One 4 Health Ltd | Health & social care | 2012 |
| One Business Supplies Ltd | Health & social care | 2020 |
| One Community Foundation Limited | Health & social care | 2009 |
| One Educationuk Limited | Education | 2022 |
| One Fortress Limited | Real estate | 2017 |
| One Heart One Mission C.I.C. | Health & social care | 2025 |
| One Horizon Travel Ltd | Administrative & support | 2023 |
| One Key Property Ltd | Real estate | 2025 |
| One Nova Ltd | Wholesale & retail | 2022 |
| One Point Recruitment Limited | Administrative & support | 2018 |
| One Smart Cookie Communications Limited | Professional & scientific | 2012 |
| One Source Electrical Yorkshire Ltd | Construction | 2022 |
| One Step Electrical Installations Ltd | Construction | 2026 |
| One Step Tech Ltd | Professional & scientific | 2026 |
| One Stop Commerce Ltd | Water & waste | 2022 |
| One Stop Energy Shop Limited | Construction | 2020 |
| One Stop Property Group Ltd | Real estate | 2022 |
| One Stop Station Ltd | Wholesale & retail | 2024 |
| One Valkyrie Group Ltd | Professional & scientific | 2022 |
| One Voice Design Consultancy Limited | Professional & scientific | 2002 |
| ONE14FIVE Limited | Health & social care | 2018 |
| Onealiff Limited | Wholesale & retail | 2021 |
| Onefast Logistics Ltd | Transport & logistics | 2022 |
| Onehd Innovations Limited | Financial services | 2024 |
| Onestac Limited | Wholesale & retail | 2026 |
| Onestop ICT Limited | Wholesale & retail | 2024 |
| Onewildcard Ltd | Information & communication | 2024 |
| Onfigr Limited | Information & communication | 2023 |
| Onitech Ltd | Manufacturing | 2024 |
| Online Forever Ltd | Wholesale & retail | 2015 |
| Online Medical Exams Limited | Other services | 2011 |
| Onlineironing.Com LP | | 2014 |
| Onlineretailers Ltd | Wholesale & retail | 2023 |
| ONLINESHOP4ALLSORTS Ltd | Wholesale & retail | 2020 |
| Onopoli Limited | Real estate | 2024 |
| Onpoint Powerpoint Limited | Information & communication | 2015 |
| Onside Travel Management Limited | Professional & scientific | 2024 |
| Onthespott Ltd | Wholesale & retail | 2025 |
| Ontrack Auto Care Ltd | Wholesale & retail | 2026 |
| Onwards Festival Ltd | Arts & recreation | 2024 |
| Onyx Hospitality Limited | Hospitality | 2010 |
| Onyx Noir Limited | Wholesale & retail | 2025 |
| Opaio Limited | Information & communication | 2023 |
| Opal White Ltd | Health & social care | 2023 |
| OPE Design Limited | Wholesale & retail | 2019 |
| Open 2 Design Ltd | Professional & scientific | 2007 |
| Open House Huddersfield Limited | Other services | 2019 |
| Open House Hudds & South Leeds Ltd | Other services | 2026 |
| Open Law Ltd | Professional & scientific | 2019 |
| Opendentist Ltd | Health & social care | 2025 |
| Opened Ltd | Education | 2019 |
| Opinicus Ltd | Information & communication | 2021 |
| Opportunities Opened CIC | Education | 2025 |
| Opsflow Facilities Ltd | Administrative & support | 2026 |
| Optic EYE Wear Ltd | Wholesale & retail | 2016 |
| Optima 3D Limited | Professional & scientific | 2018 |
| Optima Labs Ltd | Information & communication | 2025 |
| Optimal Digital Solutions Limited | Professional & scientific | 2020 |
| Optimal FT Limited | Real estate | 2024 |
| Optimal Places Limited | Real estate | 2024 |
| Optimax Services Ltd | Water & waste | 2025 |
| Optimise Living Ltd | Real estate | 2026 |
| Optimo Strategy Ltd | Professional & scientific | 2025 |
| Optimum 500 Ltd | Administrative & support | 2013 |
| Optimum Storage Systems Limited | Construction | 1991 |
| Optitel UK Ltd | Construction | 2020 |
| Optx Limited | Health & social care | 2022 |
| Opulent Beds Limited | Wholesale & retail | 2020 |
| Opulent Cakes Ltd | Manufacturing | 2025 |
| Opulent Odyssey Ltd | Wholesale & retail | 2023 |
| Opus Motion Ltd | Transport & logistics | 2024 |
| Oracle Wealth Ltd | Financial services | 2011 |
| Oragyms Ltd | Arts & recreation | 2017 |
| Oral Shine Limited | Health & social care | 2018 |
| Orange Quarter Ltd | Manufacturing | 2020 |
| Orchard Property Developments Limited | Construction | 2024 |
| Orchid Assisted Living Limited | Health & social care | 2022 |
| Order Delivery Solutions Ltd | Transport & logistics | 2026 |
| Orezy Enterprise Limited | Wholesale & retail | 2025 |
| Organic Adventure Ltd | Arts & recreation | 2025 |
| ORGANICSEO4U Limited | Extraterritorial | 2018 |
| Oriental Taste Huddersfield Ltd | Hospitality | 2021 |
| Original Accessories Ltd | Wholesale & retail | 2016 |
| Original Monk Ltd | Manufacturing | 2026 |
| Ornamental Aquatics Wholesale Limited | Wholesale & retail | 2020 |
| Ortho-Medical-Legal Ltd | Health & social care | 2020 |
| Ortholegal Consulting Ltd | Professional & scientific | 2025 |
| Orthopaedic & Trauma Services Limited | Health & social care | 2002 |