| Op-tec Systems Ltd | Stockport | A rating |
| OPA BATH LTD | BATH | A rating |
| Opal Banqueting Ltd | Smethwick | A rating |
| Opal BPM Limited | London | A rating |
| Opal Care Homes Limited | Birmingham | A rating |
| OPAL CONSULTANCY LTD | BRENTWOOD | A rating |
| Opal Food Processing Systems Limited | St Ives | A rating |
| OPAL TRADERS LIMITED | Walton on Thames | A rating |
| Opal Wave Solutions Ltd | London | A rating |
| Opal22 Arts and Edutainment | Leicester | A rating |
| Opaleye and Middlefell Limited | Gloucester | A rating |
| OpalTec International Limited | Bristol | A rating |
| OPAS GROUP LTD | Gosport | A rating |
| Opay Holding Limited | St Albans | A rating |
| Opcare Limited | Abingdon | A rating |
| Opde UK Limited | London | A rating |
| OPEC CBRNe ltd | Warrington | A rating |
| Opecprime Development Ltd | London | A rating |
| Opella Healthcare UK Limited | Reading | A rating |
| Open all Hours | Morecambe | A rating |
| Open Arms Care Limited | Faversham | A rating |
| OPEN BIONICS LTD | BRISTOL | A rating |
| Open Box Software Limited | Rochester | A rating |
| Open Cages Advocacy Ltd | Sutton | A rating |
| OPEN CLIMATE FIX LIMITED | London | A rating |
| Open College Network London Region | London | A rating |
| Open Cosmos Limited | DIDCOT | A rating |
| Open Creates LTD | London | A rating |
| OPEN CREDIT LIMITED | LONDON | A rating |
| Open Data Services Cooperative Limited | Manchester | A rating |
| Open Date Equipment Limited | Mitcham | A rating |
| Open Destinations Limited | London | A rating |
| Open Development And Education Ltd | Barnet | A rating |
| OPEN DOOR YOUNG PEOPLE'S CONSULTATION SERVICE | LONDON | A rating |
| Open Doors Housing & Support Ltd | Coventry | A rating |
| Open Doors International Inc. | Witney | A rating |
| Open Doors with Brother Andrew t/a Open Doors UK & Ireland | Witney | A rating |
| Open Education AI CIC | Covent Garden | A rating |
| Open Health Communications LLP | Marlow | A rating |
| Open Heart Care Ltd | London | A rating |
| OPEN HOUSE CARE LTD | London | A rating |
| Open House Estate Agents Bedford Ltd | Bedford | A rating |
| Open House London Limited | London | A rating |
| OPEN HOUSE MCR LTD | Manchester | A rating |
| Open Hydro Ltd | London | A rating |
| Open Influence UK Limited | London | A rating |
| Open International Ltd | Worcester | A rating |
| Open Medical Ltd | Ealing | A rating |
| Open Network Systems Limited | London | A rating |
| Open Ocean UK LLP | London | A rating |
| Open Outdoor Media Ltd | Liverpool | A rating |
| Open Plan Law Limited | Oxford | A rating |
| Open Safety Equipment Ltd | Musselburgh | A rating |
| Open School Trust Ltd. | Cambridge | A rating |
| Open Science Tools Limited | Nottingham | A rating |
| Open Society Foundation London | London | A rating |
| Open Source Centre Limited | London | A rating |
| Open Space Labs UK, Limited | Reading | A rating |
| Open Synergy Limited | Farnham | A rating |
| Open Technology Services UK Limited | London | A rating |
| OPEN TEXT UK LIMITED | READING | A rating |
| Open Trade Technology Ltd | Altrincham | A rating |
| Open Utility Ltd | London | A rating |
| Open Volume Studio Ltd | London | A rating |
| Open World 2 Limited | Romford | A rating |
| OPEN WORLD FINANCIAL SERVICES LTD | London | A rating |
| OPEN22 SOLUTIONS LIMITED | Barking | A rating |
| OpenAI UK Ltd | London | A rating |
| OpenBet Limited | London | A rating |
| Openborder recruitment Limited | LANARK | A rating |
| Opencast Software Europe Limited | Newcastle-Upon-Tyne | A rating |
| OPENCOREOS UK LTD | London | A rating |
| OpenCorporates Ltd | London | A rating |
| openDemocracy Limited | London | A rating |
| OpenDialog AI Limited | London | A rating |
| OpenESG Platform Ltd | London | A rating |
| OpenGamma Limited | London | A rating |
| OPENORIGINS LIMITED | London | A rating |
| Openpay UK Ltd | London | A rating |
| OpenPayd Holdings Ltd | London | A rating |
| Openplay Limited | Chilworth | A rating |
| OPENQUERY LTD | London | A rating |
| Opensee Limited | London | A rating |
| OPENSHAW SUPERSTORE LIMITED | Manchester | A rating |
| OpenSignal Limited | London | A rating |
| Opensoft Systems Ltd | Knaresborough | A rating |
| OPENSOFT TECHNOLOGIES LIMITED | Worcester Park | A rating |
| OPENSOLAR UK LTD | Devon | A rating |
| OpenSymmetry Consulting Limited | London | A rating |
| OpenTable International Limited | London | A rating |
| Openwave Systems Ltd. | Belfast | A rating |
| Openweather LTD | London | A rating |
| Openweather Ltd. | London | A rating |
| Openwide Coastal ltd | Cromer | A rating |
| Openwork Services Limited | Swindon | A rating |
| OpenX Limited | London | A rating |
| OPERA AYLESBURY LIMITED | Luton | A rating |
| Opera Gallery Group Limited | London | A rating |
| Opera Holland Park | London | A rating |
| Opera North Ltd | Leeds | A rating |
| OPERA PRODUCTION LTD | Christchurch | A rating |
| Opera Rara | London | A rating |
| Operation Goldeneye Ltd | Bishopton | A rating |
| Operation Mobilisation | Oswestry | A rating |
| Operation Orphan | Nottingham | A rating |
| Operational Research in Health Limited | Reading | A rating |
| Operational Solutions Ltd | Reading | A rating |
| Operations Helix Ltd | Glasgow | A rating |
| Operations Nation Ltd | Bedford | A rating |
| Operations.Finance Limited | London | A rating |
| Operexx Ltd | London | A rating |
| OPERIS GROUP PLC | LONDON | A rating |
| Opes Financial Partners Ltd | London | A rating |
| Opet International Ltd | London | A rating |
| OPH Telford Ltd | Telford | A rating |
| Opheem Ltd | Birmingham | A rating |
| Ophelos Ltd | London | A rating |
| Opia Limited | London | A rating |
| Opinium Research LLP | London | A rating |
| Opinr UK Software Limited | London | A rating |
| OPIS ON PHARMACEUTICAL INDUSTRY SERVICE UK LTD | London | A rating |
| OPJ SERVICES LTD | Plymouth | A rating |
| OPKITCHEN LTD | London | A rating |
| Oplog UK Limited | London | A rating |
| Oplyse Holdings Limited | London | A rating |
| OPM UNIVERSAL SOLUTIONS LIMITED | Manchester | A rating |
| Opmobility Exterior UK Limited | Measham | A rating |
| Oponee CONSULTING AND CONSTRUCTION LTD | Wolverhampton | A rating |
| OPP Programme Office Ltd | Oxford | A rating |
| Oppenheimer Europe Ltd | London | A rating |
| Oppenheimer Generations Services UK Limited | London | A rating |
| OPPERMANN LONDON LTD | London | A rating |
| Oppida Estates Ltd | London | A rating |
| Oppizi UK Limited | London | A rating |
| Oppo Brothers Ltd | London | A rating |
| Oppo Cars Ltd | Dagenham | A rating |
| OPPO CARS LTD | Romford | A rating |
| Opportunity Green | London | A rating |
| Opportunity International UK | Oxford | A rating |
| OPPW Limited | Rugeley | A rating |
| OPR Services Ltd | London | A rating |
| OPRE Solutions Ltd | London | A rating |
| OPS Structures Ltd | Cirencester | A rating |
| OPS Wines Ltd | LONDON | A rating |
| Opsec Security Limited | Washington | A rating |
| OPSECURED LTD | LONDON | A rating |
| OPSERV LTD | Croydon | A rating |
| OPSES LIMITED | Hampshire | A rating |
| Opsmatix Systems Ltd | London | A rating |
| Opsmorph | London | A rating |
| OPSO LTD | London | A rating |
| Opsyte Online | Farnborouh | A rating |
| Optagon Ltd | Coventry | A rating |
| Optal Financial Limited | London | A rating |
| Optalis Ltd | Wokingham | A rating |
| OPTALITIX | London | A rating |
| Optalysys Ltd | Leeds | A rating |
| Optceutics Ltd | London | A rating |
| Optegra UK Ltd | Edgware | A rating |
| Optellum Limited | Oxford | A rating |
| Opteo Ltd | London | A rating |
| Optera Solutions Limited | Manchester | A rating |
| Opteran Technologies Ltd | Sheffield | A rating |
| Optex Europe Ltd | Maidenhead | A rating |
| OPTI REACH LTD | London | A rating |
| Optiat Ltd | London | A rating |
| Optibrium Ltd | Cambridge | A rating |
| Optibus Transportation Limited | London | A rating |
| Optical Center UK Ltd | London | A rating |
| Optical Express Limited | Glasgow | A rating |
| Optical Fiber Packaging Ltd | Haverhill | A rating |
| Optical Metrology Services LTD | Stansted | A rating |
| Optical Support Ltd | London | A rating |
| OPTICAL WORLD SOUTHALL LTD | SOUTHALL | A rating |
| Opticare Opticians | Holywood | A rating |
| Opticlear Ltd T/A iCare Centre | Luton | A rating |
| Opticore IT Limited | London | A rating |
| Opticum Ltd | London | A rating |
| OPTIfarm | CHESTERFIELD | A rating |
| OPTIFARM LTD | Chesterfield | A rating |
| Optigenomics Limited | Oxford | A rating |
| Optility Limited | Birmingham | A rating |
| Optilogic UK Ltd | Birmingham | A rating |
| OPTIM SYSTEM LTD | Baldock | A rating |
| Optima Accountants Ltd | Cardiff | A rating |
| OPTIMA CARE GROUP LLP | WEST ON SUPERMARE | A rating |
| Optima Consulting Partners Limited | London | A rating |
| Optima Contracting Ltd t/a Optima Architectural Glass (OAG) | High Wycombe | A rating |
| Optima Energy Systems Limited | Manchester | A rating |
| Optima HCI Limited | Ipswich | A rating |
| Optima Health and Social Care Ltd | Denton | A rating |
| Optima Health UK Limited | Sheffield | A rating |
| Optima Law Solicitors Ltd | Slough | A rating |
| Optima Management Limited | Watford | A rating |
| Optima Medical Limited | Guildford | A rating |
| Optima Partners Limited | Edinburgh | A rating |
| Optima Training & Consultancy Limited | Harlow | A rating |
| OPTIMAL BITS LIMITED | London | A rating |
| Optimal Build Ltd | London | A rating |
| Optimal Chiropractic & Wellness Centre LTD | Cardiff | A rating |