| North Furniture Ltd | Manufacturing | 2005 |
| Northwick Park Trust | Education | 2014 |
| Nothings Holy Limited | Financial services | 2019 |
| Nova Plant Hire Ltd | Construction | 2023 |
| NR Consulting Group Ltd | Professional & scientific | 2026 |
| NRA Consultants Limited | Construction | 2013 |
| NRA Consulting Limited | Construction | 2015 |
| NRG Scaffolding Ltd | Construction | 2014 |
| NU Shades Ltd | Administrative & support | 2011 |
| NVW Rail Ltd | Construction | 2018 |
| NZ Sports Limited | Manufacturing | 2026 |
| O&M Electrical Contractors Limited | Construction | 2022 |
| O'Neills Enterprises Ltd | Manufacturing | 2014 |
| Oak Home Developments Limited | Construction | 2012 |
| Oakbourne Services Ltd | Other services | 2015 |
| Oakbridge Building Limited | Construction | 2025 |
| Oakleigh Letting Limited | Real estate | 2010 |
| Oakwood Claims Management Limited | Financial services | 2020 |
| OCD Finance Limited | Professional & scientific | 2012 |
| Oikos Storage Limited | Transport & logistics | 1936 |
| Olive Health and Social Care Ltd | Health & social care | 2022 |
| Olivia LYN Consulting Ltd | Professional & scientific | 2026 |
| OLY Construction Ltd | Construction | 2021 |
| OMG Haircare Ltd | Other services | 2010 |
| Omirad Services Limited | Transport & logistics | 2015 |
| ON Point Lettings and Management Ltd | Real estate | 2016 |
| One Diamond Ltd | Real estate | 2020 |
| One East Hill Limited | Construction | 1989 |
| One Stop Development Group Ltd | Construction | 2026 |
| One Stop Developments Ltd | Construction | 2025 |
| Onetime Painting Contractors Ltd | Construction | 2019 |
| Ongar Mill Limited | Information & communication | 2011 |
| ONX Scaffolding Ltd | Construction | 2026 |
| Oobeedoo Limited | Manufacturing | 2024 |
| Ooosh Design Limited | Manufacturing | 2009 |
| Opal Water Treatment Limited | Administrative & support | 2019 |
| Opaline Training Limited | Professional & scientific | 2026 |
| Oprah's Health Care Ltd | Health & social care | 2014 |
| Optical Facilities Ltd | Construction | 2020 |
| Optical Mechanical Limited | Construction | 2022 |
| Optical Plumbing and Mechanical Ltd | Construction | 2016 |
| Optimre Consulting Limited | Administrative & support | 2022 |
| Oracle Creative Media Limited | Information & communication | 2016 |
| Orange Box Theatre Group Ltd | Administrative & support | 2021 |
| Orca Scuba Diving Limited | Education | 2022 |
| Orchard Business Park Ltd | Real estate | 2017 |
| Original Inkhouse Ltd | Other services | 2013 |
| Orton Tiling Limited | Construction | 2006 |
| Otimo Property Services Ltd | Construction | 2023 |
| Oulton Broad Mini ZOO Limited | Arts & recreation | 2018 |
| Outability CIC | Other services | 2024 |
| Owen's GAS Solutions Limited | Other services | 2021 |
| Oysterfleet Ltd | Hospitality | 1994 |
| P & D Electrical Ltd | Construction | 2017 |
| P B Fruit Consultants Limited | Other services | 2013 |
| P D G Installations Limited | Construction | 2022 |
| P Gould Construction Ltd | Information & communication | 2021 |
| P J Dorrell Limited | Construction | 1995 |
| P J H Security Limited | Administrative & support | 2020 |
| P J Walsh Limited | Wholesale & retail | 2018 |
| Packham Properties Limited | Construction | 2017 |
| Paddock Sponsor Limited | Professional & scientific | 2011 |
| Palm Tree Management Ltd. | Hospitality | 1997 |
| Palm Tree Sales Limited | Administrative & support | 1999 |
| Palmer and Klein Limited | Manufacturing | 1989 |
| Palmpark Estates Limited | Real estate | 2012 |
| PAM Logistics Services Limited | Other services | 2015 |
| Panch Foron London Limited | Hospitality | 2025 |
| Papenburg Village Ltd | Real estate | 2026 |
| Paradise Court Management Company Limited | Real estate | 2010 |
| Pariflorencethomas Limited | Health & social care | 2016 |
| Paristoll Limited | Construction | 1999 |
| Parkfields Holdings Limited | Construction | 2026 |
| Partridges'Land Limited | Professional & scientific | 2001 |
| PAS Electrical & Solar Services Ltd | Construction | 2011 |
| PATIENTS2PEOPLE Limited | Health & social care | 2012 |
| Pattiswick Medical Services Limited | Administrative & support | 2021 |
| Pattiswick Support Services Limited | Administrative & support | 2021 |
| Paul Chandler Services Limited | Manufacturing | 2015 |
| Paul Coulson Consulting Ltd | Professional & scientific | 2024 |
| Paws Delights Limited | Manufacturing | 2025 |
| Pawsitive Connections CIC | Administrative & support | 2025 |
| PBL Property Holdings Ltd | Real estate | 2023 |
| PCM 247 Maintenance Limited | Construction | 2016 |
| PCM247 Properties Ltd | Real estate | 2020 |
| PCS City Group Ltd | Construction | 2024 |
| PCS Legal Limited | Other services | 2010 |
| PD Wood Construction Limited | Construction | 2025 |
| Pedro IT Limited | Information & communication | 2022 |
| Peninsular Security and Facilities Management Limited | Administrative & support | 2026 |
| People's India Limited | Hospitality | 2021 |
| Perfect Care Independent Living Limited | Health & social care | 2020 |
| Performance Training Ltd | Arts & recreation | 2015 |
| Perry Thermal Limited | Construction | 2025 |
| Peter Timms Consultancy Limited | Professional & scientific | 2018 |
| Pettafor Rental Properties Limited | Real estate | 2020 |
| PH Cladding Limited | Real estate | 2025 |
| PH Maintenance Limited | Real estate | 2025 |
| Philbri Ltd | Administrative & support | 2013 |
| Phillips Resolutions Ltd | Information & communication | 2019 |