| Openpetase CIC | Stoke-On-Trent | 2024 |
| Operate & Excavate Ltd | Newport | 2019 |
| Operational Strategy Ltd | Wymondham | 2014 |
| Opes Liverpool Ltd | Bury | 2023 |
| Opes MRF 2013 Limited | Leigh-On-Sea | 2013 |
| Opfor Pest Control Ltd | London | 2025 |
| OPO Recycling Ltd | Godalming | 2026 |
| OPS Environmental Services Ltd | Heywood | 2015 |
| Opteco UK Ltd | London | 2026 |
| Opti Plus Services Ltd | Slough | 2011 |
| Optima Professional Cleaning Services Ltd | Mansfield | 2026 |
| Optimal Enterprise Ltd | London | 2024 |
| Optimax Services Ltd | Huddersfield | 2025 |
| Optimise Waste Solutions Ltd | West Malling | 2023 |
| Optimo Waste Ltd | Glasgow | 2025 |
| Optimum Drain Limited | Portsmouth | 2023 |
| Optimum Property Group Ltd | Penzance | 2018 |
| Optimum Recycling Limited | Uxbridge | 2020 |
| Optimum Recycling Services Ltd | Hounslow | 2025 |
| Optimum Recycling Solutions Limited | Ely | 2019 |
| Optimum Waste Solutions Ltd | Plymouth | 2025 |
| Optimus Waste Ltd | London | 2025 |
| Option Business Services Limited | London | 2012 |
| Options Confidential Waste Services Limited | Sutton | 2005 |
| Opus Contracting Limited | Nottingham | 2022 |
| Opus Ferrivia Limited | Hammerwich | 2025 |
| Oracle Environmental Experts Limited | Malvern | 2014 |
| Orange Skip Limited | Wolverhampton | 2018 |
| Orange Skips (NW) Ltd | Bury | 2021 |
| Orange UK Group Ltd | Coalville | 2020 |
| Orbital Waste Solutions Ltd | Bradford | 2025 |
| Orca Environmental Ltd | London | 2022 |
| Orca Recycling Ltd | Birmingham | 2025 |
| Orcathletics Ltd. | Plymouth | 2019 |
| Orchard & Banks Ltd | Cheltenham | 2015 |
| Orchard Environmental Water Services Limited | 20/20 Business Park | 2007 |
| Orchard Furniture Recycling Ltd | Bacup | 2023 |
| Orchard Recycling Service Ltd | Longhope | 2014 |
| Orchid Environmental Limited | Thornaby | 2003 |
| Orchid Sky Recycling Limited | Chandlers Ford | 2021 |
| Orcol Limited | Ormskirk | 2024 |
| Organic Power Indonesia Limited | Templecombe | 2024 |
| Organic Recycling Limited | Peterborough | 1995 |
| Organic Waste Logistics Ltd | London | 2015 |
| Organic Waste Management (ST Helens) Ltd | Altrincham | 2005 |
| Organic Waste Management Limited | Altrincham | 2004 |
| Organic Wastes Management Limited | Somerset | 2006 |
| Organics Energy Limited | Coventry | 2017 |
| Organics Group PLC | Coventry | 2005 |
| Organics Limited | Coventry | 1999 |
| Organised Grime Ltd | Didcot | 2022 |
| Organotech Ltd | Freshwater | 2023 |
| Origicx Ltd | Malvern | 2017 |
| Origin Cleaning Ltd | St. Albans | 2000 |
| Origin Drainage Services Ltd | St. Albans | 2012 |
| Orion Demolition Limited | Harrow | 2019 |
| Orion Environmental Services Limited | Hemel Heampstead | 2019 |
| Orion WS Ltd | Coventry | 2025 |
| Orionate Limited | London | 2025 |
| Oris Waste Removal Ltd | Croydon | 2025 |
| Orixy Recycling Ltd | Nottingham | 2025 |
| Orkney Zerowaste | Kirkwall | 2005 |
| ORL Metals Ltd | Newport | 2015 |
| Ormskirk Skip Hire Ltd | Bootle | 2024 |
| Ormskirk Skip Recycling Limited | Ormskirk | 2011 |
| Ormskirk Skips Ltd | Bootle | 2023 |
| Orna Limited | London | 2023 |
| Orthios (Anglesey) Technologies Limited | London | 2018 |
| ORU Collective Ltd | London | 2026 |
| Osarch Environmental Ltd | Basildon | 2023 |
| Osborne Automotive Ltd | Diss | 2026 |
| Osbour Ltd | Deal | 2020 |
| Osca BIO Energy Ltd | Buckhurst Hill | 2017 |
| Osecopy Engineers Limited | London | 2016 |
| Osian Nuclear Limited | London | 2022 |
| Osiris Drainage Ltd | Brill | 2026 |
| Osmonds Environmental Limited | Tonbridge | 2015 |
| Osmotic Solutions Ltd | Howden | 2012 |
| Osnosh CIC | Oswestry | 2019 |
| OSO Environmental Ltd | Preston | 2019 |
| Osprey Remediation Ltd | Hatfield | 2021 |
| Ostara Europe (UK) Limited | London | 2016 |
| Oswald International Trading Limited | London | 2024 |
| Oswestry Waste Paper Limited | Tarporley | 2006 |
| OTB Reactive Services Ltd | Rayleigh | 2021 |
| Othen Enterprises Limited | Esher | 2022 |
| Otos Services Limited | London | 2004 |
| Ottan Ltd | London | 2023 |
| OUR Dignity | Dagenham | 2021 |
| OUR Flow Ltd | Cardiff | 2025 |
| OUR House Clearance Ltd | Ipswich | 2026 |
| Ourgreenroots Ltd | Leighton Buzzard | 2026 |
| Ouroboros Festival Services Limited | Dumfries | 2026 |
| OUT Safe Ltd | Witham | 2026 |
| Outer Space Genies Ltd | Portsmouth | 2026 |
| Outsource Corporation Limited | Shrewsbury | 1997 |
| Over the Air Analytics Limited | Biddisham | 2015 |
| Overflow Plumbing & Drainage Ltd | Hillingdon | 2020 |
| Oversize Tyre Recycling Ltd | Lurgan | 2022 |
| Overstock Ltd | Romford | 2026 |