| Ohana Care Group Limited | Northampton | A rating |
| Ohana Parental Assessment Centre | Grays | A rating |
| OHANNES FOOD SOLUTIONS LTD | Mansfield | A rating |
| Ohashi Technica UK Ltd | Washington | A rating |
| OHGB LIMITED | Birmingham | A rating |
| Ohlogy Ltd | London | A rating |
| OHM ELECTRICAL ENGINEERING LTD | Ilford | A rating |
| OHM Engineering Limited | Clogher | A rating |
| OHM'S LAW V=IR LTD | Gateshead | A rating |
| Ohme Operations UK Limited | London | A rating |
| OHMG (Holdings) Ltd | Newry | A rating |
| OHMG Brands Limited | Forest Row | A rating |
| Ohms and Watts (Services) Ltd | Hemel Hempstead | A rating |
| OHMSPACE LTD | Southampton | A rating |
| Oho Group Limited | London | A rating |
| OHP&BI Ltd/ trading as BIBIDA | London | A rating |
| Ohpen Services UK Limited | London | A rating |
| OHRI CONVENIENCE STORE LIMITED | Ellesmere Port | A rating |
| OHYM LTD T/A THE NINES | Belper | A rating |
| OI CREATIVE SERVICES LTD | London | A rating |
| OIA Global Ltd | Richmond | A rating |
| Oikos Family Centres Limited | Bradford | A rating |
| Oil & Gas Measurement Limited | Ely | A rating |
| Oil & Gas Systems Limited | Ely | A rating |
| Oil and Gas Authority | London | A rating |
| Oil Brokerage Limited | London | A rating |
| Oil Change UK | London | A rating |
| Oil Plus Ltd | Newbury | A rating |
| OIL STATES INDUSTRIES (UK ) LTD | NIGG | A rating |
| OIL TANKS PLUS LIMITED | Daventry | A rating |
| Oilfield Insurance Agencies Ltd | London | A rating |
| Oilfield Production Consultants (OPC) Limited | London | A rating |
| Oilgear Towler Limited | Leeds | A rating |
| OILPOINT UK LTD | Glasgow | A rating |
| Oishin Ltd T/A Spice of India | Chipping Norton | A rating |
| Oister Creative LTD | LONDON | A rating |
| OJ Solutions Services Limited | Salford | A rating |
| Oja Shops Ltd | Stratford | A rating |
| Ojas Group Ltd | Rugby | A rating |
| Ojas Immune Ltd | Oxford | A rating |
| OJAYS AUTOS LIMITED | London | A rating |
| OJC IT Limited | Newcastle Upon Tyne | A rating |
| Ojocaliente Ltd | London | A rating |
| Ok Bags (Sole Trade) | Orpington | A rating |
| Ok Barber | Bury | A rating |
| OK Bargains Ltd | Cambridge | A rating |
| OK Convenience Store Ltd | ELLESMERE PORT | A rating |
| OK Cool | London | A rating |
| OK CREATER LTD | Rochdale | A rating |
| OK Grills Ltd T/A Nom Noms | Manchester | A rating |
| OK Hospitality Ltd T/A The Taphouse Bar & Restaurant | Magherafelt | A rating |
| OK-RM Limited | London | A rating |
| OK&OK LIMITED | London | A rating |
| OKA DIRECT LTD | Abingdon | A rating |
| Oka Restaurant | London | A rating |
| Oka Restaurant Notting Hill Ltd | London | A rating |
| Okala Limited | Stirling | A rating |
| Okamura Corporation, London Branch | London | A rating |
| OKAN MEATHOUSE LTD | Urmston | A rating |
| Okapi Partners Ltd | London | A rating |
| Okara CTG Ltd T/A Bombay Tandoori Restaurant | Dereham | A rating |
| Okay Health Ltd | London | A rating |
| OKE Development Ltd | Maidenhead | A rating |
| Okehampton Medical Centre | Okehampton | A rating |
| Okehampton Road Post Office | Devon | A rating |
| Oki Europe Limited | Egham | A rating |
| OKI Europe Ltd | Egham | A rating |
| okoHaus UK Limited | Ipswich | A rating |
| Okome Ltd T/A Okome | Glasgow | A rating |
| OKONOMI LIMITED | LONDON | A rating |
| OKTA CONSTRUCTION LIMITED | London | A rating |
| Okta UK Ltd | London | A rating |
| Oktra Ltd | London | A rating |
| Okulo Ltd (Presently trading as OKKO Health) | Bristol | A rating |
| OKUS CONVENIENCE STORE LTD | Swindon | A rating |
| OKX UK FinTech Company LImited | London | A rating |
| OKYO PHARMA LTD | London | A rating |
| Ola Chiropractic Limited | Totnes | A rating |
| OLA Limited | Glasgow | A rating |
| OLA UK Private Limited | London | A rating |
| Olabamiji and Co Limited | Glasgow | A rating |
| Olam Care Services | MIddlesborough | A rating |
| Olam Europe Limited | London | A rating |
| Olam UK Business Solutions Limited | London | A rating |
| Olaniwun Ajayi (UK) LLP | London | A rating |
| Olapic UK Limited | London | A rating |
| Olaplex UK Limited | London | A rating |
| Olatunde Ashaolu & Co (UK) Ltd | London | A rating |
| Olayan Europe Limited | London | A rating |
| OLAYINKA ADERINKOLA AKINRINOLA FOUNDATION UK | LONDON | A rating |
| Olayinka Bukola | Reading | A rating |
| OLC College Limited | Manchester | A rating |
| OLD BAILEY SOLICITORS | BRIGHTON | A rating |
| Old Barn Stores | North Waltham | A rating |
| Old Bridge Surgery | Looe | A rating |
| Old Burlington Spirit Limited | London | A rating |
| Old Catton Medical Practice | Norwich | A rating |
| Old Chang Kee UK Limited | London | A rating |
| Old Chilly Pictures Ltd | Sheffield | A rating |
| Old Church Store | Coventry | A rating |
| OLD ELIZABETHANS CRICKET CLUB | WORCESTER | A rating |
| Old Empire Ltd | Great Wakering | A rating |
| Old Fire Station Surgery | Beverley | A rating |
| Old Fletton Surgery | Peterborough | A rating |
| Old Forge Surgery Annalong | Annalong | A rating |
| Old Friends Care ltd | Redditch | A rating |
| OLD HENRY STREET MC LIMITED | Leigh | A rating |
| Old Hill Cricket Club | Cradley Heath | A rating |
| OLD KENT MINI STORE LTD | London | A rating |
| Old Lion Pailton Ltd T/A The Old Lion | Rugby | A rating |
| Old MacDonald's Day Nursery Ltd. | Bovingdon | A rating |
| Old Mill Road Minimarket Ltd | Saffron Walden | A rating |
| Old Mill Veterinary Practice | Stornoway | A rating |
| Old Mission Europe LLP | London | A rating |
| Old Northamptonians Cricket Club | Northampton | A rating |
| Old Oak and Park Royal Development Corporation | London | A rating |
| Old Oak cafe | London | A rating |
| OLD ORCHARD CLINIC (SUSSEX) LIMITED | Eastbourne | A rating |
| Old Owens Cricket Club | Potters Bar | A rating |
| OLD PLAZA LTD | Manchester | A rating |
| OLD RECTORY CARE LTD | PINNER | A rating |
| Old Rectory Nursing Home Ltd | Capenhurst | A rating |
| Old Road West Surgery | Gravesend | A rating |
| Old Roundabout Store | Liverpool | A rating |
| Old Rutlishians Cricket Club | London | A rating |
| Old School Barbers | London | A rating |
| OLD SCHOOL HOUSE | LONGWICK | A rating |
| Old School House Surgery | Great Bedwyn | A rating |
| Old Silhillians Hockey Club, The Old Silhillians Associaton Limited | Solihull | A rating |
| Old Square Dental Practice Partnership (Ravi Panesar) | Warwick | A rating |
| Old Stone Ltd T/A Old Stone Vets | Alston | A rating |
| Old Swan Health Centre Group Practice | Liverpool | A rating |
| Old Thorns Golf Hotel & Country Estate Ltd | Griggs Green | A rating |
| OLD TOWN CONVENIENCE LTD T/A One Stop | Kingston Upon Hull | A rating |
| OLD TOWN EXPRESS LTD T/A Day Today | Edinburgh | A rating |
| Old Town Stores Limited | Hastings | A rating |
| OLD TUDOR HALL LIMITED | HITCHIN | A rating |
| Old Vicarage Ltd | Neath | A rating |
| Old Vicarage Registered Care Home Ltd | Llangollen | A rating |
| Old Vicarage School Trust | Richmond upon Thames | A rating |
| Old Village Wine Shop | Manchester | A rating |
| Old White Hart | Oakham | A rating |
| Old Whitgiftians Cricket Club | Croydon | A rating |
| Old Wilsonians' Cricket Club | Bromley | A rating |
| Old Windsor Dental Practice | Old Windsor | A rating |
| OLD WULFRUNIANS TETTENHALL CRICKET CLUB | WOLVERHAMPTON | A rating |
| Oldara Ltd (Cleeve Wood Pharmacy) | Bristol | A rating |
| Oldbourne & Oldbourne Hospitality Ltd trading as L'oscar London Hotel | London | A rating |
| Oldbury Energy Solutions Ltd | Oldbury | A rating |
| Oldendorff Carriers (UK) Ltd | London | A rating |
| Oldercare (Haslemere) Limited | Haslemere | A rating |
| Olderfleet Hotel Limited | Larne | A rating |
| Olderiswiser Media Limited | London | A rating |
| Oldfield Residential Care Ltd | Bridgnorth | A rating |
| Oldfield School | BATH | A rating |
| OLDFORD CONVENIENCE STORE LIMITED | London | A rating |
| Oldford Farms Ltd | Stafford | A rating |
| Oldham Athletic (2004) Association Football Club Limited | Oldham | A rating |
| Oldham Bethel Church | Oldham | A rating |
| Oldham Business & Construction Management Ltd | Oldham | A rating |
| Oldham Council | Oldham | A rating |
| Oldham Engineering LImited | Sheffield | A rating |
| Oldham Family Practice | Oldham | A rating |
| Oldham Food Store Limited | Oldham | A rating |
| Oldham GHCSRC | OLDHAM | A rating |
| Oldham Groceries UK Ltd t/a Oldham Superstore | Oldham | A rating |
| OLDHAM KEBAB, PERI PERI LIMITED | oldham | A rating |
| Oldham Rugby League Football Club 1876 Limited | Oldham | A rating |
| Oldham service centre | Oldham | A rating |
| Oldhams of Westcliff Ltd | Westcliff | A rating |
| OLDWAY HEIGHTS LTD | Paignton | A rating |
| Ole Ole Lincoln Limited | Lincoln | A rating |
| Olea Care Ltd | Stockport | A rating |
| Olenick Global Ltd | Belfast | A rating |
| Oleochem Project Management Ltd | Aberdeen | A rating |
| Oleon Ltd. | Northallerton | A rating |
| Olfnet Ltd | Manchester | A rating |
| OLGA TV | London | A rating |
| Olimp Laboratories UK Ltd | London | A rating |
| Olio at The Chequers Ltd | Wickham Bishops | A rating |
| OLIO Exchange Limited | London | A rating |
| Oliva Health Limited | London | A rating |
| OLIVALIS CONSULTING LTD | London | A rating |
| Olivares Ltd | Lincoln | A rating |
| Olive Academies | Hornchurch | A rating |
| Olive and Tree Limited | West Bromwich | A rating |
| Olive Banquet Ltd T/A Aurum Restaurant | Southend-on-Sea | A rating |
| Olive Base Ltd | London | A rating |
| Olive Bedford LTD | bedford | A rating |
| OLIVE CARE SOLUTIONS LTD | Peterborough | A rating |
| Olive Farmer Ltd T/A Skewers | London | A rating |
| Olive Grove Canterbury Limited T/A Olive Grove | Canterbury | A rating |
| OLIVE HEALTH & TRAVEL LTD | London | A rating |
| Olive Hemel Limited | HERTFORDSHIRE | A rating |
| Olive Leaf Health & Homecare Limited | Bristol | A rating |
| Olive Legal Associates Ltd | Bradford | A rating |
| OLIVE N PERI PERI LTD T/A Perifellas | London | A rating |
| Olive of Sinai (Preston) Ltd | Preston | A rating |
| OLIVE PATHWAY | Manchester | A rating |
| Olive Technologies Ltd | Reading | A rating |