| Millwood Court Management Company Limited | Real estate | 1988 |
| Milton Partnership Limited | Construction | 2021 |
| Mindful Arts Ltd | Health & social care | 2011 |
| Ming WAH 888 Ltd | Hospitality | 2021 |
| Mini Robin Ltd | Wholesale & retail | 2015 |
| Mission Radio Love Music Love Life Ltd | Wholesale & retail | 2024 |
| Mission Zero Group Limited | Transport & logistics | 2021 |
| Mithril Limited | Professional & scientific | 2017 |
| Mivi Store Ltd | Wholesale & retail | 2025 |
| MJM Research and Development Ltd | Information & communication | 2023 |
| MJN Letchworth Ltd | Real estate | 2013 |
| MK RAI Ventures Limited | Real estate | 2026 |
| Mmann Properties LLP | | 2017 |
| Mmce Consulting Ltd | Professional & scientific | 2019 |
| MNJ Consulting Ltd | Information & communication | 2006 |
| MNY UK Limited | Wholesale & retail | 2008 |
| Mobile EAR Care Ltd | Health & social care | 2025 |
| Mobile Magic Ltd | Administrative & support | 2017 |
| Mochic Ltd | Wholesale & retail | 2020 |
| Modern People Limited | Administrative & support | 2026 |
| Mokida Office Admin Limited | Administrative & support | 2018 |
| Mokovision Limited | Information & communication | 2005 |
| Monarch GB Ltd | Wholesale & retail | 2005 |
| Money Rocket Ltd | Professional & scientific | 2023 |
| Moneyspider Mortgages Limited | Financial services | 2007 |
| Moneyspyder Digital Services Ltd | Information & communication | 2019 |
| Montague Lodge Limited | Real estate | 2024 |
| Montalt Partners Ltd | Administrative & support | 2024 |
| Montone Twenty Ltd | Financial services | 2025 |
| Moor Park Investments Limited | Real estate | 2018 |
| Moore Stone Interiors Limited | Construction | 2021 |
| Mopheth Financial Services Limited | Professional & scientific | 2017 |
| Mopheth Healthcare Limited | Health & social care | 2022 |
| Moregem Ltd | Administrative & support | 2024 |
| Morris Grips Limited | Information & communication | 2012 |
| Morris Investment and Property Limited | Real estate | 2015 |
| Morris-Spicer Ltd | Construction | 2021 |
| Mortimer & Nautilus Ltd | Real estate | 2021 |
| Moss Jaguar Limited | Wholesale & retail | 2013 |
| Motor Magic Vehicle Services Limited | Wholesale & retail | 2020 |
| Motorcycle Pitstop Ltd | Professional & scientific | 2025 |
| Motorlogic Ltd | Wholesale & retail | 2023 |
| Move Total Infrastructure Ltd | Professional & scientific | 2024 |
| Moving Through Life CIC | Health & social care | 2017 |
| Moyrence Ltd | Health & social care | 2019 |
| MR Infinity Limited | Real estate | 2024 |
| Msar Group Limited | Real estate | 2025 |
| Msov Electrical Ltd | Construction | 2023 |
| MTO Ductwork Ltd | Construction | 2024 |
| Multiple Sclerosis Trust (Trading) Limited | Wholesale & retail | 1993 |
| Munya & Munashe Investments Limited | Health & social care | 2015 |
| Murfitts Industries Limited | Manufacturing | 2000 |
| Murraydata Limited | Information & communication | 2008 |
| MUU Creative Ltd | Professional & scientific | 2019 |
| Muve Gym Ltd | Arts & recreation | 2025 |
| MW Decorating Services Ltd | Construction | 2016 |
| MW Khan Limited | Administrative & support | 2023 |
| MW Utilities Limited | Energy | 2023 |
| My Candle Moments Ltd | Wholesale & retail | 2025 |
| My Fitness Hub Limited | Arts & recreation | 2014 |
| My Health & Wellness Ltd | Health & social care | 2023 |
| My Language Hub Ltd. | Professional & scientific | 2016 |
| My Party Store Ltd | Hospitality | 2025 |
| Mymoby.Ai Ltd | Information & communication | 2025 |
| N.A.J Brothers Ltd | Wholesale & retail | 2026 |
| N.M.F. Management Limited | Real estate | 1959 |
| Najae Kalie Ltd | Health & social care | 2021 |
| Nanny Julie's Ltd | Other services | 2017 |
| Napier Court Limited | Real estate | 2019 |
| Nasmyth CRC Ltd. | Health & social care | 2022 |
| National Office of Animal Health Limited | Professional & scientific | 1987 |
| Navatar Ltd | Information & communication | 2017 |
| Navex Limited | Information & communication | 2011 |
| NAZ Spice Ltd | Hospitality | 2018 |
| NBS Solutions Ltd | Real estate | 2017 |
| Ncsmd Ltd | Health & social care | 2025 |
| ND Autos Ltd | Wholesale & retail | 2011 |
| Need&Buy Ltd | Wholesale & retail | 2023 |
| NEG Surveying Ltd | Construction | 2025 |
| Nemland Ltd | Information & communication | 2025 |
| Nerdbunch Limited | Information & communication | 2025 |
| Nessies Chilminding Limited | Education | 2019 |
| Nevells Road Management Company Limited | Households | 2005 |
| New Cloud Solutions Limited | Information & communication | 2019 |
| New Holland Group Ltd | Manufacturing | 2025 |
| New Inn Farm Silsoe Limited | Real estate | 2024 |
| New Light Services Limited | Professional & scientific | 2004 |
| Nexa Store UK Ltd | Wholesale & retail | 2024 |
| Nexgen Security Solutions Limited | Administrative & support | 2025 |
| Nextron Solutions Limited | Wholesale & retail | 2026 |
| Nhclean Limited | Administrative & support | 2022 |
| Nightingale Court (Hitchin) Management Company Limited | Households | 1991 |
| Nightingale Press Limited | Manufacturing | 1972 |
| Nimble Solutions Limited | Wholesale & retail | 2008 |
| Nine One Two Nine Ltd | Real estate | 2020 |
| Nintclass Ltd | Wholesale & retail | 2023 |
| Nitdas Ltd | Public administration | 2026 |
| NKS Complaints Limited | Administrative & support | 2013 |
| No-Radgarage Ltd | Wholesale & retail | 2023 |
| Nobleland Limited | Real estate | 1988 |