| One Call Plumbing & GAS Services Ltd | Construction | 2024 |
| One Call Rescue Limited | Other services | 2008 |
| One Call Taxis 247 Ltd | Transport & logistics | 2022 |
| One Continent Ltd | Real estate | 2023 |
| One Dream Living Limited | Real estate | 2025 |
| One Eleven Management Company Limited | Real estate | 2002 |
| One Health Group Trustees LLP | | 2014 |
| One Hundred Stars Trading Limited | Wholesale & retail | 2014 |
| One Insulation Ltd | Construction | 2020 |
| One Lakeside Limited | Construction | 2023 |
| One Market Square Management Company Limited | Households | 2014 |
| One Million Monkeys Ltd | Professional & scientific | 2021 |
| One Mind Limited | Hospitality | 2015 |
| One NIL Away Limited | Information & communication | 2014 |
| One Oak Development Limited | Construction | 2014 |
| One Park Rise Ltd | Real estate | 2025 |
| One Records Limited | Administrative & support | 2018 |
| One Shop Stop Ltd | Wholesale & retail | 2024 |
| One Spot Supplies Limited | Wholesale & retail | 2021 |
| One Step Lingual Services Ltd | Professional & scientific | 2023 |
| One Step Mini Market Ltd | Wholesale & retail | 2026 |
| One Stop Mot's Ltd | Wholesale & retail | 2025 |
| One Stop Professional Building Contractors Ltd | Water & waste | 2018 |
| One Stop Properties (Sheffield) Limited | Real estate | 2008 |
| One Stop Roofing Centre Limited | Extraterritorial | 1990 |
| One Stop Solutions Consultants Limited | Professional & scientific | 2018 |
| One Stop Study Ltd | Education | 2025 |
| One Stop Tax Limited | Professional & scientific | 1999 |
| One Stop Tyre Services Ltd | Wholesale & retail | 2020 |
| One Stop Valeting Limited | Administrative & support | 2025 |
| One to One Community Care Limited | Health & social care | 2012 |
| One Two Three Property Management Limited | Households | 2025 |
| One World Supermarket Ltd | Wholesale & retail | 2024 |
| One Zero 7EVEN Media Ltd | Information & communication | 2021 |
| One-Step Security Services Limited | Administrative & support | 2024 |
| One.Three. Eyewear Ltd. | Other services | 2026 |
| ONE2CALL Limited | Administrative & support | 2007 |
| ONE9SEVEN Development Ltd | Information & communication | 2020 |
| Onebutton Limited | Wholesale & retail | 2005 |
| Onecare Academy Ltd | Education | 2024 |
| Onelife Healthcare Ltd | Public administration | 2021 |
| Onenineeightfour Limited | Arts & recreation | 2007 |
| Onesacre Ltd | Manufacturing | 2022 |
| Onesphere IT Solution Services Ltd | Information & communication | 2025 |
| Onetechelectronics Limited | Manufacturing | 2013 |
| Onfour Ltd | Manufacturing | 2022 |
| ONI Legal Ltd. | Professional & scientific | 2020 |
| Onik News Limited | Information & communication | 2026 |
| Onioncube Limited | Information & communication | 2023 |
| Onisiforou Ltd | Transport & logistics | 2025 |
| Oniu Scientific Limited | Professional & scientific | 2021 |
| Online Accountancy and Finance Limited | Professional & scientific | 2020 |
| Online Advertising Productions Limited | | 2009 |
| Online Flooring and Beds Limited | Wholesale & retail | 2014 |
| Online Group Services Ltd | Construction | 2009 |
| Online Holdings INT. Ltd | Financial services | 2018 |
| Online Holiday Bookings UK Ltd | Administrative & support | 2018 |
| Online Leisure UK Ltd | Wholesale & retail | 2020 |
| Online Magic Ltd | Wholesale & retail | 2021 |
| Online Payments Limited | Financial services | 2011 |
| Only Clay Limited | Arts & recreation | 2021 |
| ONLY30 Limited | Professional & scientific | 2016 |
| ONN Financial Limited | Real estate | 2025 |
| Onosom Distribution Limited | Wholesale & retail | 2022 |
| Onotech Ltd | Manufacturing | 2020 |
| Onpodium Productions Limited | Information & communication | 2024 |
| Onsei DM Limited | Health & social care | 2021 |
| Onside Sports Ltd | Professional & scientific | 2012 |
| Onsight Audio Ltd | Information & communication | 2025 |
| Onslow House Residents Limited | Real estate | 2014 |
| Onurball.Com Ltd | Arts & recreation | 2025 |
| Onvid Ltd | Information & communication | 2021 |
| Onwa International Limited | Wholesale & retail | 2021 |
| Onyix Digital Ltd | Professional & scientific | 2023 |
| Onyva Ltd | Health & social care | 2009 |
| Onyx Cutz Ltd | Other services | 2026 |
| Onyx Vision Ltd | Wholesale & retail | 2024 |
| OOH Shiny! Ltd | Extraterritorial | 2009 |
| Ooozu Limited | Wholesale & retail | 2013 |
| Oops to Awesome Ltd | Education | 2026 |
| OP Management Ltd | Transport & logistics | 2023 |
| OP Realisations Limited | Construction | 1979 |
| Opal Contracting Ltd | Professional & scientific | 2023 |
| Opal IVY Aesthetics Clinic Ltd | Health & social care | 2026 |
| Opalite Learning Ltd | Public administration | 2022 |
| Opat Homes Assets Ltd | Real estate | 2023 |
| OPC Technology Limited | Information & communication | 2004 |
| Open Gates Outdoors (Community) CIC | Arts & recreation | 2023 |
| Open Hands Project (Sheffield) | Hospitality | 2007 |
| Open House Architecture Ltd | Professional & scientific | 2023 |
| Open House Pictures Limited | Information & communication | 2018 |
| Open House Project Limited | Construction | 2012 |
| Open Research Shop Ltd | Information & communication | 2023 |
| Open Space Medical Support Ltd | Health & social care | 2022 |
| Open UP Sheffield | Arts & recreation | 2003 |
| Openarch AM Research Ltd | Manufacturing | 2026 |
| Openclass H.E Ltd | Education | 2025 |
| Opensky Technologies Ltd | Information & communication | 2025 |
| Opensource Commercial and Procurement Services Ltd | Information & communication | 2025 |
| Operation YOU Ltd | Education | 2025 |