| MLR Distribution Ltd | Construction | 2021 |
| MMS (Oxfordshire) Limited | Extraterritorial | 2011 |
| MMS Business Limited | Professional & scientific | 2005 |
| MO Financial Consulting Ltd | Information & communication | 2017 |
| Modern Edge Decorating Ltd | Construction | 2026 |
| Modus Accountants Limited | Professional & scientific | 2017 |
| Modus Developments Limited | Real estate | 2016 |
| Modus Investments Limited | Extraterritorial | 2020 |
| Mofford Projects Limited | Construction | 2024 |
| MOL Flights Limited | Administrative & support | 2005 |
| MOL Holdings Limited | Financial services | 2019 |
| Momenta Newcastle Ltd | Health & social care | 2019 |
| Monarch Hose and Hydraulics Ltd | Wholesale & retail | 2005 |
| Monarch Properties Solutions Ltd | Real estate | 2026 |
| Monerium UK Limited | Information & communication | 2020 |
| Monica Main Method Ltd | Education | 2026 |
| Monk Papelier Ltd | Arts & recreation | 2025 |
| Monkscroft Advisory Ltd | Professional & scientific | 2025 |
| Mont Blanc Projects Limited | Professional & scientific | 2021 |
| Moonbeam Tech Limited | Information & communication | 2022 |
| Moondog&Co Ltd | Information & communication | 2024 |
| Moonlight Mobile Limited | Administrative & support | 2011 |
| Moora Motors Limited | Wholesale & retail | 2026 |
| Moorfield Partners Limited | Professional & scientific | 2025 |
| Moose Automotive Design Limited | Professional & scientific | 1989 |
| Morego Mechanical Limited | Wholesale & retail | 2006 |
| Moreton on the Square Ltd | Hospitality | 2020 |
| Morgan Gibaud Associates Limited | Real estate | 1994 |
| Morgen HR Limited | Professional & scientific | 2005 |
| Morningfields Growth Partners Ltd | Professional & scientific | 2025 |
| Morrell Place Management Ltd | Households | 2020 |
| Morris Weston Investments Ltd | Real estate | 2019 |
| Morse Motors Limited | Wholesale & retail | 2012 |
| Mortgage Capacity Consultants Ltd | Financial services | 2023 |
| Mortis Ltd | Real estate | 2023 |
| Moshon Data Limited | Professional & scientific | 2013 |
| Moshon Limited | Professional & scientific | 2013 |
| Mosim Limited | Health & social care | 2021 |
| Mostro Coffee Ltd | Hospitality | 2022 |
| Motifyme Ltd | Wholesale & retail | 2025 |
| Motobase Ltd | Extraterritorial | 2022 |
| Motorfix (Witney) Limited | Wholesale & retail | 2004 |
| Motorpart Logistics Limited | Wholesale & retail | 2021 |
| Mount Olympus Properties Ltd | Real estate | 2023 |
| Moveya Holdco Limited | Financial services | 2026 |
| Moveya Limited | Information & communication | 2026 |
| Moyolo Travel Ltd | Administrative & support | 2025 |
| Mpack UK Ltd | Wholesale & retail | 2015 |
| MPR Johnson Limited | Transport & logistics | 2025 |
| Mpwood Ltd | Health & social care | 2025 |
| MR a to B Ltd | Wholesale & retail | 2025 |
| Mr-Triathlon Ltd | Administrative & support | 2017 |
| MRB Builders Limited | Construction | 2019 |
| MRM Solutions Ltd | Professional & scientific | 1997 |
| MS Civil Engineering Ltd | Construction | 2015 |
| MSD Surgical Services Ltd | Health & social care | 2019 |
| MSR Oxford Limited | Hospitality | 2006 |
| MT and Sons Roofing and Building Ltd | Construction | 2020 |
| MTD Cloud Accounting Limited | Extraterritorial | 2018 |
| MTS Property Developments Ltd | Real estate | 2025 |
| Mtvm Boreham Wood Limited | Financial services | 2025 |
| Mtvm Capital Limited | Financial services | 2025 |
| Mubu Properties Ltd | Real estate | 2016 |
| Mukhiya Group Ltd | Financial services | 2026 |
| Mukhiya Limited | Real estate | 2024 |
| Mulberry Housekeeping Ltd | Administrative & support | 2025 |
| Mulbor Holdings Limited | Real estate | 2022 |
| Mullcross Investments Limited | Real estate | 2025 |
| Mullins Holding Company Limited | Financial services | 2025 |
| Multiplant Limited | Manufacturing | 2003 |
| Mungo and Associates Limited | Extraterritorial | 2020 |
| Munique Enterprises Ltd | Professional & scientific | 2014 |
| Murtry Barn SPV Ltd | Real estate | 2025 |
| Muzoakademy II CIC | Wholesale & retail | 2022 |
| My Futures Investment & Trading (Myfit) Ltd | Other services | 2021 |
| My Khana Box Ltd | Hospitality | 2026 |
| Mybarberapp Limited | Information & communication | 2026 |
| Mycostrategist Limited | Professional & scientific | 2024 |
| Mynopoly Dreams Ltd | Real estate | 2017 |
| Mynydd Portref Limited | Energy | 2008 |
| Mynydd Windfarm LLP | | 2011 |
| Myplayservice Limited | Information & communication | 2016 |
| Myriad Life Solutions Ltd | Information & communication | 2024 |
| Mysa at Home Limited | Extraterritorial | 2023 |
| Mysmeleader Ltd | Administrative & support | 2024 |
| Mystic Games Ltd | Wholesale & retail | 2021 |
| N a Godfrey ( Builders) Limited | Construction | 2002 |
| N a Godfrey (Training) Limited | Construction | 2012 |
| N-Kohs Ltd | Real estate | 2021 |
| N. Van Muijlwijk Estates Ltd | Hospitality | 2025 |
| N.B Equestrian Ltd | Agriculture & fishing | 2018 |
| N.C.C.B.R. Stonesfield Limited | Wholesale & retail | 2001 |
| N.Lutton Ltd | Manufacturing | 2025 |
| N.T. Laboratories Holdings Limited | Financial services | 2026 |
| Nabarro and Sons Ltd | Real estate | 2026 |
| Nagresco Properties Ltd | Construction | 2018 |
| Nanophoton Technologies Limited | Professional & scientific | 2007 |
| Narrowing the Gaps Ltd | Manufacturing | 2011 |
| Natal Landscapes Ltd | Administrative & support | 2020 |
| National Refrigeration Services Ltd | Wholesale & retail | 2020 |