| OM International | Administrative & support | 2005 |
| OM International Services (Carlisle) Limited | Administrative & support | 2015 |
| Omddms Ltd | Information & communication | 2022 |
| Omega Car and Commercial Ltd | Wholesale & retail | 2020 |
| OMK Limited | Hospitality | 2022 |
| Omnis Solutions Limited | Information & communication | 2007 |
| Omrt Properties Limited | Real estate | 2024 |
| Once Upon a Dog Ltd | Other services | 2021 |
| One 2 Tree Surgery Ltd | Agriculture & fishing | 2016 |
| One-O-Five Precision Ltd | Professional & scientific | 2022 |
| Onlinemedia.Co.Uk Limited | Professional & scientific | 2002 |
| Onunda Limited | Manufacturing | 2022 |
| Oopsie Daisy Flowers Limited | Wholesale & retail | 2023 |
| Open Esco Limited | Construction | 2025 |
| Open Heat Network Limited | Construction | 2025 |
| Open Space (Cumbria) Limited | Professional & scientific | 2003 |
| OPERATIONAL.SOLUTIONS2026 Limited | Professional & scientific | 2026 |
| Ophir Road House Limited | Households | 2025 |
| OPS and Tech Consultants Limited | Real estate | 2010 |
| Optech Electrical Solutions Ltd | Construction | 2018 |
| Optergo Ltd | Manufacturing | 2022 |
| Optimisation Business & Construction Consultants Ltd | Construction | 2024 |
| Optimum Cleanrooms Ltd | Construction | 2011 |
| Oracle Clinics Northumberland Ltd | Health & social care | 2026 |
| Orchard Investments (UK) Limited | Other services | 2016 |
| Orchard Ladders Limited | Manufacturing | 2019 |
| Orchard Place (Appleby) Flat Management Company Limited | Households | 2018 |
| Orchard Place (Appleby) Management Company Limited | Households | 2015 |
| Orchard Tree Surgery Ltd | Agriculture & fishing | 2018 |
| Oreal Consulting Ltd | Information & communication | 2018 |
| Orego Limited | Information & communication | 2000 |
| Orian Solutions Limited | Administrative & support | 2012 |
| Origins Caterers Limited | Hospitality | 2013 |
| Orrdone Farms Limited | Agriculture & fishing | 2015 |
| Orton Grange Cafe & Gifts Limited | Hospitality | 2014 |
| Orton Grange Wind Energy Limited | Administrative & support | 2012 |
| Orton Park Renewable Energy Limited | Energy | 2013 |
| OSM Partners Ltd | Wholesale & retail | 2026 |
| Ostri Ltd | Wholesale & retail | 2025 |
| Otac Trading Ltd | Wholesale & retail | 2016 |
| Ottersons Limited | Construction | 2020 |
| Ottimo Bikes Limited | Manufacturing | 2013 |
| OUR Happyhippo Ltd | Real estate | 2023 |
| Outdoor Learning Services Ltd | Administrative & support | 2018 |
| Outreach Cumbria Limited | Administrative & support | 2012 |
| Oval Court Management Limited | Households | 2004 |
| Overbuilt UK Ltd | Wholesale & retail | 2026 |
| Overwater Design and Marketing Limited | Manufacturing | 2011 |
| Overwater Hotels Limited | Hospitality | 1992 |
| Owen Armstrong Properties Limited | Real estate | 2025 |
| Owen’S Drives and Patios Ltd | Construction | 2026 |
| OWL & Seggie Property Group Ltd | Real estate | 2025 |
| OWL & Smith Limited | Real estate | 2025 |
| OWL 5D Property Group Limited | Real estate | 2025 |
| OWL Lets & Management Limited | Real estate | 2025 |
| OWL Options & Investments Ltd | Administrative & support | 2016 |
| OWL Properties North Limited | Real estate | 2021 |
| Ozchelik Ltd | Hospitality | 2025 |
| P & S Barker Property Management Ltd | Real estate | 2022 |
| P & S Miller Limited | Real estate | 2011 |
| P and E Blythe Ltd | Wholesale & retail | 2021 |
| P E & M Capstick Ltd | Agriculture & fishing | 2015 |
| P E Advertising Limited | Professional & scientific | 2024 |
| P Ferry Training Ltd | Construction | 2025 |
| P Hopper Properties Ltd | Real estate | 2017 |
| P J Cumbria Ltd | Construction | 2015 |
| P J Developments (Cumbria) Limited | Construction | 2024 |
| P LEE Waste Management Limited | Water & waste | 2024 |
| P M Makar Ltd | Transport & logistics | 2018 |
| P MCD Couriers Ltd | Transport & logistics | 2023 |
| P Purdham Ltd | Transport & logistics | 2010 |
| P Senior Limited | Administrative & support | 2020 |
| P T Bell & SON Limited | Wholesale & retail | 2012 |
| P W Temple Limited | Construction | 1998 |
| P&M Douglas Properties Limited | Construction | 2017 |
| P-Hygeine Services Ltd | Construction | 2025 |
| P. Coates (Cumbria) Ltd | Agriculture & fishing | 2012 |
| P. Harris & SON Limited | Construction | 2005 |
| P. LEE (Waste Oils) Limited | Water & waste | 1998 |
| P.F.D.(Carlisle)Limited | Wholesale & retail | 1955 |
| P.H.S.M. Limited | Administrative & support | 2008 |
| P5 Garments Ltd | Wholesale & retail | 1982 |
| P@T Test Ltd | Manufacturing | 2021 |
| PA Cloud Ltd | Administrative & support | 2017 |
| Packhorse Bridge Management Company Limited | Households | 2002 |
| Padan Consulting Ltd | Professional & scientific | 2025 |
| Paddaburn Ltd | Other services | 2022 |
| Paddock View Lettings Ltd | Households | 2025 |
| Padthaistreat Ltd | Professional & scientific | 2012 |
| Page & Wick Ltd | Wholesale & retail | 2023 |
| Page (Carlisle) Limited | Hospitality | 2014 |
| Palace Holdings Ltd | Financial services | 2026 |
| Palmer Renewables Limited | Energy | 2014 |
| Palmpro Limited | Professional & scientific | 2003 |
| Panashe Logistics Ltd | Transport & logistics | 2013 |
| Pandellium Ltd | Information & communication | 2021 |
| Pants and Socks Limited | Wholesale & retail | 2020 |
| Papillon Care Limited | Health & social care | 2002 |
| Pappan Limited | Hospitality | 2002 |
| Paprika Carlisle Limited | Hospitality | 2022 |