| Mieco Limited | Professional & scientific | 2012 |
| Mildenhall Speedway Supporters CIC | Arts & recreation | 2025 |
| Military Equipment Specialists Ltd | Wholesale & retail | 2021 |
| Mill Reef Residents Company Limited | Households | 2007 |
| Milton Investors Ltd | Hospitality | 2018 |
| Mimica LAB Ltd | Professional & scientific | 2017 |
| Mindful Global Leadership Ltd | Professional & scientific | 2025 |
| Minha Casa Ltd | Real estate | 2025 |
| Mintt Ltd | Wholesale & retail | 2021 |
| Miramodel Ltd | Hospitality | 2026 |
| MJ Beauty Newmarket Ltd | Other services | 2024 |
| MJ Ltd | Extraterritorial | 2024 |
| MKR Logistics Limited | Transport & logistics | 2026 |
| Mks-T Consultancy Limited | Professional & scientific | 2012 |
| MM Fresh Produce Support Services Ltd | Other services | 2014 |
| MM Hair Design & Beauty Ltd | Other services | 2020 |
| Mmmi Logistics Ltd | Transport & logistics | 2022 |
| MMS Renovations & Property Services Ltd | Construction | 2025 |
| MNT Hospitality Ltd | Hospitality | 2024 |
| MO Ltd | Extraterritorial | 2009 |
| Moatwood Properties Limited | Construction | 2014 |
| MOH Consultancy Ltd | Professional & scientific | 2024 |
| Mohamad Moubarak Racing Ltd | Administrative & support | 2016 |
| Mokaccino Ltd | Hospitality | 2025 |
| Molyneux Business Park Ltd | Real estate | 2014 |
| Monkey Puzzle House Music Publishing Limited | Arts & recreation | 2016 |
| Montague Consulting Ltd | Professional & scientific | 2011 |
| Montcastle Bloodstock Limited | Agriculture & fishing | 2016 |
| Monty Adamson Ltd | Professional & scientific | 2019 |
| Monty Life Sciences Limited | Professional & scientific | 2020 |
| Moonlightshadow Ltd | Wholesale & retail | 2025 |
| Moons Dental Limited | Health & social care | 2019 |
| Moor Green Engineering Ltd | Professional & scientific | 2023 |
| Moose Holdings Ltd | Real estate | 2021 |
| Morecroft Developments Limited | Construction | 2019 |
| Morgan Geen Investments Limited | Real estate | 2016 |
| Morgan-Evans Equestrian (UK) Limited | Arts & recreation | 2011 |
| Morgan-Evans Equestrian Limited | Agriculture & fishing | 2013 |
| Morgan-Evans Property Ltd | Real estate | 2021 |
| Morgan-Vega Vision Ltd | Health & social care | 2021 |
| Mornett Brickwork and Construction Limited | Construction | 2025 |
| Morris Armitage Limited | Real estate | 2002 |
| Morris Residential Investments Limited | Financial services | 2017 |
| Morris Safe Storage Solutions Limited | Real estate | 2025 |
| Morsfell Limited | Professional & scientific | 1996 |
| Morshead Bloodstock Limited | Arts & recreation | 2026 |
| Motorhedz Ltd | Administrative & support | 2024 |
| Moulton Manor Farm (Holdings) Limited | Agriculture & fishing | 1994 |
| MP Limited | Extraterritorial | 2008 |
| MR Greek Food Ltd | Hospitality | 2023 |
| MR. Fothergill's Seeds Limited | Manufacturing | 1983 |
| MRM Media Productions Limited | Manufacturing | 2025 |
| MSL Plume PUB Co Ltd | Hospitality | 2024 |
| MT Ltd | Extraterritorial | 2024 |
| MU Limited | Extraterritorial | 2007 |
| Muirpace Holdings Limited | Professional & scientific | 1985 |
| Muirpace Limited | Extraterritorial | 1981 |
| Multicraft Electrical Services Limited | Construction | 2008 |
| Multicraft Group Ltd | Construction | 2021 |
| Multicraft Mechanical and Electrical Services Ltd | Construction | 2022 |
| Murray Park Management Company Limited | Households | 2005 |
| Muse Fine Art Limited | Professional & scientific | 2023 |
| Music My JAM CIC | Arts & recreation | 2025 |
| Musks Food Group Limited | Manufacturing | 1999 |
| Musks Limited | Manufacturing | 1993 |
| Mustard Bloodstock Limited | Professional & scientific | 2010 |
| Mustard Music Studio Ltd | Education | 2026 |
| MWB Publishing Limited | Information & communication | 2011 |
| Mwnw Investment Ltd | Extraterritorial | 2015 |
| MX Ltd | Extraterritorial | 2020 |
| My Mind News Limited | Information & communication | 2022 |
| Myracehorse Holdings Ltd | Arts & recreation | 2022 |
| Myracehorse I Ltd | Arts & recreation | 2022 |
| Myracehorse II Ltd | Arts & recreation | 2022 |
| Myracehorse III Ltd | Arts & recreation | 2022 |
| Myracehorse Investments Ltd | Arts & recreation | 2022 |
| Myracehorse IV Ltd | Arts & recreation | 2022 |
| Myracehorse Services Ltd | Professional & scientific | 2021 |
| Myracehorse V Ltd | Arts & recreation | 2022 |
| Myracehorse VI Ltd | Arts & recreation | 2022 |
| Myracehorse VII Limited | Arts & recreation | 2022 |
| N Bird Construction Limited | Construction | 2023 |
| N G Marketing Limited | Professional & scientific | 2005 |
| N G Woodworking Ltd | Manufacturing | 2025 |
| N R Financial Services Ltd | Financial services | 2019 |
| N W Accountancy (NKT) Limited | Professional & scientific | 2014 |
| N W Accountancy Limited | Professional & scientific | 2022 |
| N:Compass Create Limited | Administrative & support | 2015 |
| Nala Property Limited | Real estate | 2023 |
| Natalma Bloodstock Limited | Agriculture & fishing | 2019 |
| National Horseracing Museum(The) | Arts & recreation | 1981 |
| Nautilus (Training & Management) Ltd | Professional & scientific | 2005 |
| NC Ltd | Extraterritorial | 2009 |
| NE Ltd | Extraterritorial | 2009 |
| Nearctic Bloodstock Limited | Agriculture & fishing | 2023 |
| Nearctic Management UK Limited | Professional & scientific | 2025 |
| NEH Cotswolds Ltd | Professional & scientific | 2022 |
| Neil Picture Holdings Limited | Information & communication | 2025 |
| Neil Publishing Limited | Information & communication | 2025 |
| Nene Packaging Limited | Manufacturing | 1994 |