| Oracle Fire Sprinklers Limited | Wellington | 2022 |
| Oracle Fire Suppression Ltd | Wellington | 2022 |
| Orbita Trade N Services Limited | Oldham, United Kingdom | 2026 |
| Orchard Eyecare Limited | Armagh | 2020 |
| Orchard Fire Protection Limited | Richmond | 2022 |
| Orchids Respite Services Ltd | Doncaster | 2019 |
| Orchidvale Consultancy Ltd | Bedlington | 2014 |
| Ordna Consultancy Ltd | London | 2025 |
| Ordna Ltd | London | 2024 |
| Organise Your Life Ltd | Leamington Spa | 2023 |
| Orges Lengu Ltd | London | 2019 |
| ORI Healthcare Ltd | Andover | 2024 |
| Oriade Limited | Bournemouth | 2020 |
| Origin Social Care Solutions Ltd | London | 2023 |
| Orinthia Academy Ltd | Enfield | 2023 |
| Orion Group Holdings Ltd | London | 2025 |
| Orion Homecare Management Ltd | Fareham | 2025 |
| ORK Mena Consulting Ltd | London | 2023 |
| Orobosa Limited | Bristol | 2022 |
| ORR Specialist Fire Surveys Limited | Glasgow | 2025 |
| Ortus Fire Construction Ltd | Orpington | 2021 |
| Orzola Fire Limited | Sittingbourne | 2020 |
| OS Fire Limited | Pontypridd | 2026 |
| Osaje Services Limited | Luton | 2023 |
| Osaretin Limited | Swindon | 2023 |
| OSB Pharma Ltd | Manchester | 2021 |
| Oscar Gregson TM Ltd | Doncaster | 2025 |
| Oscar LEO T.M Ltd | Doncaster | 2025 |
| Oseaan Limited | London | 2022 |
| OSH Partners Ltd | Liverpool | 2023 |
| Osifo Recruitment Ltd | Cardiff | 2020 |
| Osler Safety Limited | London | 2021 |
| Osprey Healthcare Academy UK Limited | Romford | 2023 |
| OSS Enviro (Global) Limited | Stone | 2022 |
| Osteoandspinal Ltd | Stockport | 2022 |
| Ostomycare Limited | Belfast | 2021 |
| OT-123 Ltd | Manchester | 2024 |
| Otetela Health Ltd | Maidstone | 2020 |
| Othdabere High Quality Healthcare Services Ltd | London | 2026 |
| Otium on Demand Limited | Newport | 2024 |
| Ouch First AID Training Ltd | Henley-In-Arden | 2011 |
| Ouedraogo Limited | London | 2023 |
| OUR Angels Homecare Services Limited | Hemel Hempstead | 2025 |
| OUR Harmony Hub CIC | Eastleigh | 2025 |
| OUR Home Day Centre Ltd | Heanor | 2026 |
| OUR House of Movement Ltd | London | 2025 |
| OUR Time ALL Ability Youth Forum C.I.C. | London | 2024 |
| OUR Voice Service CIC | London | 2025 |
| Outpatient Healthcare Services Ltd | London | 2019 |
| Overcome Aesthetics Limited | Peterborough | 2023 |
| Overseas Pakistani Club Ltd | Manchester | 2022 |
| OW Energetics Ltd | Wolverhampton | 2022 |
| Owais Medical Group Limited | Birmingham | 2025 |
| Oxford Academy of Management Ltd | Oxford | 1997 |
| Oxford Business Centre Ltd | London | 2021 |
| Oxford Consultancy Partnership Limited | Witney | 2007 |
| Oxford Education Centre Ltd | Oxford, | 2023 |
| Oxford Fire Extinguishers Ltd | Witney | 2022 |
| Oxford for Postgraduate and Research College Ltd | London | 2025 |
| Oxford Guardians Limited | Northampton | 2009 |
| Oxford Professional Education & Certification Ltd | London | 2022 |
| Oxford Women Community CIC | Oxford | 2026 |
| Oxfordshire Fire Extinguishers Ltd | Witney | 2022 |
| OYE OYE Company Limited | Enfield | 2022 |
| Oyeyemi.Ogungbure Healthcare Limited | Northampton | 2022 |
| Oziyke Business Services Limited | Ilford | 2017 |
| Ozone Security Service Ltd | | 2003 |
| P & P Protective Coatings Limited | Middlesbrough | 2023 |
| P & S Gradwell Limited | Newcastle Upon Tyne | 2003 |
| P Asumadu Social Care Limited | South Ockendon | 2022 |
| P Carton Limited | Middlesborough | 2003 |
| P K Daffu Ltd | Nottingham | 2022 |
| P&R Global Consultancy Limited | London | 2024 |
| P.A. Fire Systems Limited | Chichester | 2012 |
| P.B.C. Solutions Limited | London | 2018 |
| P.F. Fire Services Limited | Wragby | 2024 |
| P1 Property Solutions Limited | Ilford | 2022 |
| P4PROGRESSION Limited | London | 2024 |
| PAA Plus 1 Ltd | Erith | 2019 |
| PAB Safety Services Limited | Middlesbrough | 2016 |
| Pace Fire Ltd | Nottingham | 2018 |
| Pace Health Ltd | London | 2023 |
| Paediatric Care Solutions Ltd | London | 2025 |
| Page Fire Protection Limited | Bury | 2003 |
| Paggarwal Pharma Limited | Teddington | 2025 |
| Pagoda Chinese Youth and Community Centre C.I.C. | Liverpool | 2020 |
| PAI Healthcare Ltd | Chesham | 2018 |
| Paige Healthcare Services Ltd | London | 2023 |
| Paisley Care Ltd | Walsall | 2024 |
| PAL Square Physio Ltd | Basingstoke | 2020 |
| Paladin Client Management Ltd | Manchester | 2022 |
| Paladin Defence Ltd | Malvern | 2025 |
| Paladin TAC Limited | London | 2014 |
| Palestone Limited | Grimsby | 2009 |
| Palladium Advisory Recruitment Ltd | Walsall | 2024 |
| Palm Tree Consultants Ltd | Cardiff | 2022 |
| Palmer Fire Ltd | Exeter | 2022 |
| Palms and Peacocks Limited | Wisbech | 2014 |
| Palmyra Health Care Solutions Ltd | Willenhall | 2023 |
| PAN African Network for One Health Consultancy Limited | Hounslow | 2024 |