| Menolicious Ltd | Administrative & support | 2025 |
| Menopause Couch Ltd | Health & social care | 2023 |
| Merchable Ltd | Wholesale & retail | 2025 |
| Merik Ltd | Manufacturing | 2014 |
| Metalogic Holdings Limited | Professional & scientific | 2007 |
| Metropolis Dynamics Limited | Information & communication | 2010 |
| Mexblue Consulting Ltd | Professional & scientific | 2022 |
| Michelle Ovens Ltd | Professional & scientific | 2007 |
| Milestone Environmental Limited | Water & waste | 2015 |
| Millar Close (Benson) Management Company Limited | Households | 2007 |
| Millercott Holdings Ltd | Professional & scientific | 2025 |
| Millington Investments Limited | Real estate | 1973 |
| Mine Tech Services (UK) Limited | Mining & quarrying | 2014 |
| Ministry of Content Ltd | Information & communication | 2019 |
| Minscombe Properties Limited | Construction | 1966 |
| Mint Management Co. Limited(The) | Professional & scientific | 1980 |
| Minta Events Ltd | Hospitality | 2022 |
| Miramar Communications Limited | Professional & scientific | 2008 |
| Mixbox Mart Ltd | Wholesale & retail | 2025 |
| ML Storyboards Limited | Other services | 2020 |
| MLS Talent Ltd | Administrative & support | 2021 |
| MMR Group Limited | Professional & scientific | 1999 |
| MMR Healthcare Limited | Professional & scientific | 2000 |
| MMR Research Group Ltd | Professional & scientific | 2000 |
| MNS Kids Limited | Education | 2013 |
| Modern Lawn Care Ltd | Administrative & support | 2022 |
| Moebeer Ltd | Wholesale & retail | 2026 |
| Mojo Events Limited | Administrative & support | 2023 |
| Mongewell Cottage Properties LLP | | 2016 |
| Montague Wharf Limited | Real estate | 2024 |
| Mooreprop Limited | Real estate | 2019 |
| Moreton Road Properties Limited | Construction | 1961 |
| Morgan Cleo Property Limited | Real estate | 2018 |
| Morph HR Ltd | Administrative & support | 2019 |
| Morrison Research Limited | Professional & scientific | 2006 |
| Mortimer Brewing Company Ltd | Manufacturing | 2018 |
| Moulsford Medical Limited | Health & social care | 2019 |
| Moulsford Preparatory School Trust Limited | Education | 1966 |
| Mountain Mania Cycles (Wallingford) Ltd | Wholesale & retail | 2017 |
| MS Truck Expert Ltd | Wholesale & retail | 2019 |
| MT Professional Services Ltd | Administrative & support | 2022 |
| MTS & Sons Investments Limited | Real estate | 2004 |
| Mulberry Bay Limited | Real estate | 2015 |
| Mullins (Reading) Limited | Construction | 2002 |
| Murgatroyd London Limited | Other services | 2025 |
| MWC Partners Limited | Information & communication | 2012 |
| My @ Solutions Ltd. | Professional & scientific | 2012 |
| My Studio (Architects) Ltd | Professional & scientific | 2022 |
| Myrtis Limited | Construction | 2006 |
| N&J Investments Holdings Ltd Ltd | Real estate | 2025 |
| N&K Window Cleaning Ltd | Administrative & support | 2018 |
| Nawaz Property Management ( Oxford ) Limited | Real estate | 2025 |
| NCT (Investment) Limited | Real estate | 2003 |
| Nest Design & Projects Ltd | Other services | 2007 |
| Netco Ltd | Real estate | 2019 |
| Network Art Ltd | Information & communication | 2025 |
| Neuromonitoring Matters Limited | Health & social care | 2020 |
| New Convenience Retailing Limited | Professional & scientific | 2018 |
| New Time Hospitality Ltd | Hospitality | 2021 |
| New Wave Wellness Ltd | Manufacturing | 2025 |
| Next Bigger Better C.I.C. | Professional & scientific | 2011 |
| Nexus Technical Services Group Ltd | Information & communication | 2023 |
| Nick Wilkins Limited | Information & communication | 2010 |
| Njesh Services Limited | Health & social care | 2022 |
| NO.25 Benson Ltd | Hospitality | 2020 |
| Normantas Ltd | Professional & scientific | 2023 |
| Norries Drive Amenity Land Limited | Other services | 2009 |
| Norton Carpentry & Construction Southern Limited | Manufacturing | 2026 |
| NPG (Benson) Ltd | Professional & scientific | 2014 |
| Nuffield Salvage Co.Limited | Water & waste | 1960 |
| NW Electrical Services Ltd | Construction | 2020 |
| Nyama Catering Limited | Hospitality | 2004 |
| O.P.E.N. Education Network | Education | 2013 |
| Oatlands House Management Limited | Households | 2010 |
| Ocean Fish & Chips Shop Ltd | Hospitality | 2021 |
| Oceanalysis Ltd | Professional & scientific | 2011 |
| Oceanis Solutions Limited | Information & communication | 2007 |
| OGM Autos Limited | Wholesale & retail | 2025 |
| Old Laundry Place Limited | Health & social care | 2019 |
| Omnicrest Limited | Financial services | 1992 |
| One Tribe Ltd. | Wholesale & retail | 2019 |
| Onimix Ltd | Wholesale & retail | 2025 |
| Onpoint Research Ltd | Administrative & support | 2018 |
| Onward HR Limited | Professional & scientific | 2013 |
| Open Limits Limited | Administrative & support | 2002 |
| Opening Doors Consultancy Ltd | Professional & scientific | 2020 |
| OPM Building Services Ltd | Construction | 2022 |
| OPO Creative Ltd | Professional & scientific | 2020 |
| OPS Apps Ltd | Information & communication | 2014 |
| OPS Qual Ltd | Professional & scientific | 2020 |
| Opus Online Services Ltd | Other services | 2024 |
| Oral Cosmetics Limited | Health & social care | 1983 |
| Orbll Ltd | Information & communication | 2025 |
| ORC Fieldwork Services Limited | Professional & scientific | 2006 |
| Organic Wine Company Limited(The) | Wholesale & retail | 1985 |
| Original Flying Chef Services Ltd | Hospitality | 2007 |
| Orsomjobs Ltd | Administrative & support | 2023 |
| Osaegis Limited | Information & communication | 2020 |
| Osirian Consulting Limited | Administrative & support | 2000 |
| Osirian Group Limited | Administrative & support | 2003 |