| Onelcon Electric & Control Systems Ltd | Manufacturing | 2019 |
| Online Coaching AMP Ltd | Arts & recreation | 2020 |
| Only Mot's Ltd | Wholesale & retail | 2026 |
| ONU Properties (GB) Ltd | Real estate | 2025 |
| Open Technology Ltd | Wholesale & retail | 2006 |
| Opsytech Ltd | Information & communication | 2016 |
| Optimal Financial Consultancy Ltd | Financial services | 2024 |
| Optimum Advertising Ltd | Professional & scientific | 2012 |
| Optimum Property Developments Limited | Real estate | 2003 |
| Optimum Sourcing Ltd | Professional & scientific | 2026 |
| Opuluxe Events Limited | Administrative & support | 2026 |
| OR Parcels Limited | Transport & logistics | 2021 |
| ORA Garden Rooms Ltd | Construction | 2023 |
| ORA Gardens Ltd | Administrative & support | 2013 |
| Orange BOY Art Ltd | Arts & recreation | 2025 |
| Orbis Novum Ltd | Manufacturing | 2021 |
| Orcaspaces Ltd | Construction | 2018 |
| Orchard (Hassocks) Residents Association Limited(The) | Households | 1967 |
| Orchard Practice Limited | Health & social care | 2016 |
| Osborne House Burgess Hill Limited | Households | 2017 |
| Oskar DIX Motorsports Limited | Arts & recreation | 2024 |
| Osprey Automotive Limited | Transport & logistics | 2018 |
| Osprey House (Hellingly) Limited | Households | 2011 |
| Osqa Limited | Professional & scientific | 2013 |
| OTE Recruitment Group Ltd | Information & communication | 2018 |
| OTR Property Management Ltd | Real estate | 2024 |
| Ottafield Court (Haywards Heath) Limited | Households | 1959 |
| Ottmann LUX Limited | Administrative & support | 2022 |
| OUT the Park Group Limited | Administrative & support | 2023 |
| Oval Accountants Ltd | Professional & scientific | 2024 |
| Ovalbar Ltd | Professional & scientific | 2010 |
| Ovalmere (1993) Limited | Financial services | 1981 |
| Ovalmere Management Ltd | Real estate | 2004 |
| Ovalmere Property Development Co. Limited | Real estate | 1987 |
| Overcomers Healthcare Limited | Health & social care | 2012 |
| OWL Electrical Limited | Information & communication | 2021 |
| Oxford Business Development Ltd | Professional & scientific | 1995 |
| Oxis International Ltd | Professional & scientific | 2024 |
| Ozen Barber Ltd | Other services | 2016 |
| P&S Property Ltd | Real estate | 2020 |
| P.P.F. (Art) Limited | Wholesale & retail | 2005 |
| P.Prosser Boiler Services Ltd | Construction | 2013 |
| P.R. Roofing Ltd | Construction | 2012 |
| Paddock Walk Management Company Limited | Households | 2024 |
| Pain and Neuromodulation Specialists Ltd | Health & social care | 2020 |
| Palmwood Limited | Professional & scientific | 2011 |
| Pamoja Productions Limited | Information & communication | 2025 |
| Pangram Limited | Professional & scientific | 2025 |
| Paper Plus Education Supplies Ltd | Wholesale & retail | 2021 |
| Park Cameras Group Limited | Administrative & support | 2013 |
| Park Cameras Holdings Limited | Real estate | 2006 |
| Park Cameras Limited | Wholesale & retail | 1979 |
| Park Court Maintenance Company Limited | Households | 1958 |
| Parker & Bartley Solutions Ltd | Construction | 2013 |
| Parker Project Management Limited | Professional & scientific | 2022 |
| Parkside Residents Association (Burgess Hill) Limited | Households | 1990 |
| Partners in Development Limited | Education | 2000 |
| Passion LDN Ltd | Other services | 2018 |
| Patterns Records Ltd | Arts & recreation | 2024 |
| Paul Drake Limited | Professional & scientific | 2004 |
| Paul Mitchell Investment Reviews Ltd | Financial services | 2017 |
| Pavilion Car Rental Ltd | Administrative & support | 2011 |
| PBE Electrical Limited | Construction | 2013 |
| PBT Electrical & Maintenance Limited | Construction | 2012 |
| PC Card Technology PLC | Extraterritorial | 1996 |
| Pcdc Decorating Services LLP | | 2026 |
| Pcjnpubs Ltd | Hospitality | 2022 |
| PDP Electrical Services Limited | Extraterritorial | 2016 |
| PDP Services Limited | Construction | 2003 |
| Peach Bite Socials Ltd | Professional & scientific | 2025 |
| Pemak Limited | Health & social care | 2013 |
| Peony Fashion Ltd | Wholesale & retail | 2024 |
| Peper Harow Limited | Wholesale & retail | 2012 |
| Pepler Communications Limited | Administrative & support | 2017 |
| Pepler LEE Group Limited | Administrative & support | 2017 |
| Pepler LEE Limited | Professional & scientific | 2018 |
| Perfect Panes Hassocks Limited | Administrative & support | 2022 |
| Perfect Properties Sussex Ltd | Extraterritorial | 2022 |
| Periastron Ltd | Professional & scientific | 2018 |
| Perryfield Court Management Company Limited | Households | 1989 |
| Personify Fitness Ltd | Arts & recreation | 2018 |
| Peter Thomas Coaching Limited | Professional & scientific | 2024 |
| Petersons Garage Limited | Wholesale & retail | 1999 |
| PF Property Ltd | Real estate | 2016 |
| PFS Computer Consultancy (Sussex) Limited | Information & communication | 1990 |
| Phase Four Ltd | Information & communication | 2025 |
| Phero Development Limited | Information & communication | 2023 |
| Philip Nash Photography Ltd | Professional & scientific | 2010 |
| Phoenix Flow Measurement Limited | Professional & scientific | 1990 |
| Phoenix House RTM Company Limited | Households | 2021 |
| Phrengo Ltd | Information & communication | 2022 |
| Physio 360 Limited | Health & social care | 2024 |
| Physio Healthy Ltd | Health & social care | 2022 |
| Physio Plus (Eastbourne) Limited | Health & social care | 2005 |
| Physio Science Global Limited | Health & social care | 2019 |
| Physio Science UK Limited | Health & social care | 2012 |
| Pier Heating Ltd | Construction | 2020 |
| Pillarbox Print Limited | Manufacturing | 2008 |
| Pilotscars (UK) Limited | Wholesale & retail | 2026 |
| Pine Trees Court Residents Association Limited | Households | 1990 |