| Nyalapogula Consultancy Services Limited | Administrative & support | 2010 |
| Nyland Graphics Limited | Wholesale & retail | 1987 |
| Nymel Day Nurseries Limited | Education | 2010 |
| NZ Estates Derby Ltd | Real estate | 2023 |
| O G Electrical Contractors Ltd | Construction | 2026 |
| O Hair by Wumi Limited | Wholesale & retail | 2026 |
| O J Godfrey Limited | Financial services | 2020 |
| O Plus K Ltd | Professional & scientific | 2017 |
| O Stevenson Ltd | Real estate | 2019 |
| O Vartan Limited | Administrative & support | 2026 |
| O&L Construction (Derby) Ltd | Construction | 2025 |
| O'Brien International Education Ltd | Education | 2023 |
| O'Connell Express Ltd | Transport & logistics | 2026 |
| O'Gelato Ltd | Hospitality | 2026 |
| O'Neill Pipework Solutions Ltd | Construction | 2014 |
| O-Kra Food (UK) Ltd | Wholesale & retail | 2016 |
| O. Heap & SON (Derby) Limited | Other services | 1979 |
| O.Phillips Limited | Construction | 2017 |
| OAH Pharma Ltd | Health & social care | 2021 |
| OAJ Medicals Limited | Health & social care | 2026 |
| Oak Avenue Investments Ltd | Real estate | 2025 |
| Oak Construction & Developments Limited | Manufacturing | 2022 |
| Oak Four Holdings Limited | Financial services | 2019 |
| Oak Four Limited | Financial services | 2016 |
| Oak Grange (Mickleton) Management Company Limited | Households | 2017 |
| Oak Healthcare Ltd | Wholesale & retail | 2010 |
| Oak Holdco 1 Limited | Financial services | 2025 |
| Oak Manor Homes Limited | Construction | 2020 |
| Oak Noir (Distribution) Ltd | Extraterritorial | 2015 |
| Oak Noir Limited | Extraterritorial | 2015 |
| Oak Tree (Lincolnshire) Care Ltd | Health & social care | 2006 |
| Oak Tree Care Group Limited | Real estate | 2021 |
| Oak Tree IP Limited | Professional & scientific | 2017 |
| Oak&Stone Estates Ltd | Real estate | 2025 |
| Oakdale Imports Ltd | Wholesale & retail | 2025 |
| Oakerstone Ltd | Real estate | 2025 |
| Oakhurst Works Limited | Real estate | 2026 |
| Oaklands (Tonbridge) Limited | Education | 2003 |
| Oaklands Bistro Limited | Hospitality | 2025 |
| Oaklands Consultants Limited | Other services | 2021 |
| Oaklands Holdings Ltd | Financial services | 2026 |
| Oaklands Park (Ashbourne) Management Company Limited | Households | 2016 |
| Oakley Consultancy Ltd | Professional & scientific | 2019 |
| Oakley Early Years Bidco Limited | Financial services | 2021 |
| Oakley Early Years Holdco Limited | Financial services | 2021 |
| Oakley Early Years Midco Limited | Financial services | 2021 |
| Oakley Early Years Topco Limited | Financial services | 2021 |
| Oakley Grange Residents Management Company Limited | Households | 2023 |
| Oakmanor Accountancy Ltd | Professional & scientific | 2014 |
| Oakoa Luxury Bespoke Interiors Limited | Construction | 2021 |
| Oakon Ltd | Administrative & support | 2026 |
| Oakridge Estates Management Ltd | Construction | 2025 |
| Oakridge People Solutions Limited | Administrative & support | 2024 |
| Oakwood Asset Holdings Ltd | Real estate | 2025 |
| Oakwood Campers Ltd | Administrative & support | 2020 |
| Oakwood Electrical & Alarms Limited | Construction | 2011 |
| Oakwood Electrical Installations Limited | Construction | 2023 |
| Oakwood Executive Cars Ltd | Transport & logistics | 2009 |
| Oakwood Garage Ltd | Wholesale & retail | 2025 |
| Oakwood Joinery and Windows Ltd | Construction | 2014 |
| Oakwood Lodge (Newchurch) Limited | Real estate | 2005 |
| Oakwood Professional Services Aiakz Ltd | Health & social care | 2026 |
| Oakwood Publishing Ltd | Information & communication | 2023 |
| Oakwood Stoves & Fireplace Installations Limited | Construction | 2008 |
| Oasis Barber Limited | Other services | 2018 |
| Oasis Bargains Ltd | Wholesale & retail | 2023 |
| Oasis Hair Products Ltd | Wholesale & retail | 2026 |
| Oasis Properties Derby Ltd | Real estate | 2026 |
| Oasis Springs Property Ltd | Real estate | 2020 |
| Oasis Takeaway (Nottingham) Limited | Hospitality | 2016 |
| Oasis-Care UK Group Limited | Professional & scientific | 2018 |
| OB Legal Ltd | Other services | 2022 |
| Obaluaye Medicals Limited | Health & social care | 2025 |
| Obara Corp. Limited | Wholesale & retail | 2016 |
| Oberoi Consulting Holdings Limited | Financial services | 2026 |
| Objectiva Ltd | Information & communication | 2009 |
| Obot International Limited | Manufacturing | 2023 |
| Obrien's Business Services Ltd | Professional & scientific | 2009 |
| OBS Couriers Ltd | Transport & logistics | 2021 |
| Obscura Hair Ltd | Other services | 2025 |
| Obsidian Management Consulting Ltd | Professional & scientific | 2026 |
| Obtainable Mortgages Limited | Financial services | 2017 |
| Occasions Catering and Deco Ltd | Hospitality | 2023 |
| Occasions Events Venue Ltd | Hospitality | 2020 |
| Occasions Venue Hire Ltd | Hospitality | 2023 |
| Occhio Vision Ltd | Health & social care | 2024 |
| OCD Property Services Ltd | Administrative & support | 2020 |
| Ocean Damage Consulting (ODC) Ltd | Professional & scientific | 2019 |
| Ocean Guard Ltd | Professional & scientific | 2025 |
| Ocean King Ltd | Wholesale & retail | 2010 |
| Ocean Property Services Ltd | Construction | 2026 |
| Ocean Pyramids Ltd | Real estate | 2025 |
| Oceanic Bounty Limited | Financial services | 2024 |
| Oceans Travel Ltd | Administrative & support | 2019 |
| Ochard Limited | Professional & scientific | 2012 |
| Ochre (Eco) Ltd | Agriculture & fishing | 2026 |
| Ockbrook Accountants Ltd | Professional & scientific | 2012 |
| Ockbrook and Borrowash Cricket Club Limited | Arts & recreation | 2025 |
| Ockbrook Construction Ltd | Construction | 2015 |
| Ockbrook Garage Doors Ltd | Construction | 2013 |