| One Removal Ltd | Transport & logistics | 2018 |
| One Revolution Initiative CIC | Education | 2024 |
| One Round at a Time Community Interest Company | Arts & recreation | 2024 |
| Onecap Limited | Professional & scientific | 2009 |
| Onegym Ltd | Arts & recreation | 2011 |
| Online Beauty Cosmetics Limited | Other services | 2018 |
| Online Digital Services Ltd | Administrative & support | 2019 |
| Onyx Apartments Management Company Limited | Households | 2015 |
| Opdoc Limited | Construction | 2016 |
| Open College Network CREDIT4LEARNING | Education | 2003 |
| Opettae VON Ltd | Wholesale & retail | 2025 |
| Opmed Healthcare Limited | Health & social care | 2023 |
| Opportuna Services Ltd | Professional & scientific | 2023 |
| Optical Outsource Ltd | Wholesale & retail | 2025 |
| Optimisation Solutions Limited | Administrative & support | 2022 |
| Optisi Ltd | Extraterritorial | 2017 |
| Optran Export Ltd | Wholesale & retail | 2025 |
| Orange PUB Co Limited | Hospitality | 2015 |
| Orbitor Performance Ltd | Manufacturing | 2025 |
| Orchard AJX Ltd | Real estate | 2024 |
| Orchard Consultant Engineering Ltd | Professional & scientific | 2023 |
| Orchard Court Owners (Darlington) Limited | Households | 1998 |
| Orchard Heating & Plumbing Ltd | Wholesale & retail | 2022 |
| Orchard Place Property Management Ltd | Households | 2017 |
| Orchard Road Brewery Limited | Hospitality | 2017 |
| Order Packaging Ltd | Extraterritorial | 2023 |
| Oreng Ltd | Professional & scientific | 2020 |
| Orex Consulting Limited | Health & social care | 2023 |
| Oriental Jasmine Therapy Spa Limited | Health & social care | 2018 |
| Origins Coffee Bar Limited | Wholesale & retail | 2014 |
| Origins Home Limited | Wholesale & retail | 2012 |
| Orolook Ltd | Wholesale & retail | 2025 |
| Oruks Homes and Properties Limited | Real estate | 2024 |
| Orukz Ltd | Construction | 2024 |
| Ostlers Court (Darlington) Management Company Limited | Real estate | 2006 |
| Otterfield Ltd | Extraterritorial | 2004 |
| Outdoor-Ambition Limited | Arts & recreation | 2007 |
| Outsourced HR Limited | Administrative & support | 2010 |
| Outstanding Cleaning Domestics Limited | Households | 2022 |
| Outstanding Installations Limited | Construction | 2015 |
| OV Leisure Ltd | Hospitality | 2025 |
| Ovegame Ltd | Wholesale & retail | 2025 |
| OW Skelton Logistics Ltd | Transport & logistics | 2025 |
| OWL Property Investments Ltd | Real estate | 2025 |
| Oxilium Ltd | Administrative & support | 2021 |
| Oxmoor Contracting Ltd | Construction | 2026 |
| Oyster and Olive Ltd | Hospitality | 2022 |
| Ozone Group Services Ltd | Real estate | 2016 |
| Ozzy's Saloon Ltd | Other services | 2023 |
| P & a Harrison Builders Limited | Construction | 2004 |
| P & V Bakers Limited | Wholesale & retail | 2011 |
| P a Designs Architects Ltd | Professional & scientific | 2011 |
| P a Designs Properties Ltd | Real estate | 2023 |
| P and a Hodges Limited | Professional & scientific | 2010 |
| P C Plumbing and GAS Ltd | Construction | 2023 |
| P C Taxis Ltd | Extraterritorial | 2017 |
| P Edwards Joinery and Building Ltd | Construction | 2019 |
| P Hunter Associates Ltd | Professional & scientific | 2019 |
| P J Hospitality Ltd | Hospitality | 2020 |
| P J R Blewitt Ltd | Construction | 2011 |
| P Lefevre Ltd. | Financial services | 2009 |
| P Mckittrick Services Ltd | Administrative & support | 2014 |
| P Mmxxi Limited | Hospitality | 2021 |
| P New GAS Services Ltd | Construction | 2022 |
| P&Ps Group Ltd | Wholesale & retail | 2018 |
| P&S Property Management Services Ltd | Real estate | 2025 |
| P.Culley Logistics Ltd | Transport & logistics | 2026 |
| P.D.N. Design & Print Limited | Manufacturing | 2000 |
| P.H. Kingsley Limited | Arts & recreation | 2003 |
| P.Hutchinson Catering Equipment Ltd | Financial services | 2014 |
| P.Windale Ltd | Real estate | 2002 |
| P2 Properties Limited | Real estate | 2022 |
| P3 Play Ltd | Education | 2024 |
| Pablo’S Property Company Limited | Real estate | 2025 |
| PAC Holdings Limited | Real estate | 1988 |
| Pac-Tec Solutions Ltd | Professional & scientific | 2009 |
| Pack Filiation Ltd | Real estate | 2024 |
| Pact Storage Ltd | Real estate | 2019 |
| Page and Screen Limited | Professional & scientific | 2005 |
| Page OR Two Ltd | Information & communication | 2020 |
| Paid Group Ltd | Financial services | 2018 |
| Paid Ltd | Extraterritorial | 2017 |
| Paid Technology Ltd | Information & communication | 2018 |
| Paint the Sky Blue Limited | Professional & scientific | 2025 |
| Palace Housing Company Ltd | Real estate | 2012 |
| Palm and Pepper Limited | Wholesale & retail | 2025 |
| Palmers Tyres Limited | Wholesale & retail | 2007 |
| Pamela's Ice Cream Van Hire Ltd | Hospitality | 2016 |
| Panda Roofing and Facades Ltd | Construction | 2025 |
| Pangmi Venture Ltd | Real estate | 2025 |
| Paradise Escapes Ltd | Administrative & support | 2025 |
| Paradise Home Improvements Limited | Households | 2025 |
| Paradise Island Getaway Lets Limited | Hospitality | 2025 |
| Paragon Rapid Technologies Ltd | Manufacturing | 2003 |
| Paramount Group NE Limited | Wholesale & retail | 2025 |
| Paraplandan Ltd | Professional & scientific | 2022 |
| Paraplanning Solutions Limited | Professional & scientific | 2011 |
| Parcel PAL Web Ltd | Transport & logistics | 2026 |
| Parcel Pushers Ltd | Transport & logistics | 2026 |
| Parcell IT Solutions Ltd | Information & communication | 2009 |