| Lugard Property Services Limited | Professional & scientific | 2008 |
| Luiza Neumayer Limited | Health & social care | 2022 |
| Lukeman Electrical Service Limited | Construction | 2023 |
| Luker Rowe & Company Limited | Financial services | 1988 |
| Luker Rowe Holdings Ltd | Professional & scientific | 2011 |
| Lumin Pathway Ltd | Education | 2002 |
| Luminate Watford Ltd | Arts & recreation | 2013 |
| Lupo Partners Ltd | Arts & recreation | 2017 |
| Luxury Briefing (London) Limited | Financial services | 2015 |
| Luxury Nails Bar Aylesbury Ltd | Other services | 2025 |
| LVD Insights Limited | Professional & scientific | 2019 |
| LVS Consulting Limited | Professional & scientific | 2003 |
| LWS Consulting Ltd | Administrative & support | 2017 |
| Lyle Developments Ltd | Hospitality | 2019 |
| Lynxwood Limited | Arts & recreation | 1996 |
| M&A Decorating Ltd | Construction | 2025 |
| M&R Laundries Limited | Other services | 2019 |
| M.S. Chahal & Sons (Wholesale) Limited | Wholesale & retail | 2004 |
| M.S. Jennings Ltd | Health & social care | 2012 |
| M.S.C. Power Limited | Wholesale & retail | 2002 |
| Maadi Enterprises Limited | Arts & recreation | 2020 |
| Machinery Mart Limited | Wholesale & retail | 2025 |
| Mackenzie Dodd Consulting Limited | Professional & scientific | 2000 |
| Madara Yoga Limited | Education | 2023 |
| Madeleine Grace Limited | Manufacturing | 2026 |
| Magic Mind Solutions Ltd | Information & communication | 2022 |
| Magnumic Ltd | Wholesale & retail | 2024 |
| Maheshwari Financials Ltd | Financial services | 2019 |
| Mahitika Ltd | Information & communication | 2024 |
| Maison Ville Deux 2 Limited | Other services | 2013 |
| Maison Ville Limited | Information & communication | 1998 |
| Majetek Limited | Real estate | 2009 |
| Majka Designs Ltd | Professional & scientific | 2023 |
| Make and Place Ltd | Wholesale & retail | 2016 |
| Malcolm Padwick Ltd | Health & social care | 2011 |
| Mall Media Finance Limited | Financial services | 2024 |
| Malone Inc Limited | Information & communication | 2022 |
| Mandala Yoga Limited | Arts & recreation | 2025 |
| Mangal Express (Little Chalfont) Ltd | Hospitality | 2016 |
| Manis Accountants Limited | Professional & scientific | 2016 |
| Manor House Style Limited | Wholesale & retail | 2025 |
| Mansil House Ltd | Real estate | 2025 |
| Mantis Advisors LLP | | 2025 |
| Marcasite Investments Limited | Real estate | 1987 |
| March 2 Limited | Real estate | 2026 |
| Maritime Operations Limited | Professional & scientific | 2020 |
| Mark Perman Web Services Ltd | Professional & scientific | 2026 |
| Mark Tudor Limited | Professional & scientific | 2013 |
| Marlow Asset Management Limited | Wholesale & retail | 2009 |
| Marlow Physiotherapy and Sports Injury Clinic Ltd | Health & social care | 2011 |
| Marrad Ltd | Professional & scientific | 2015 |
| Mars Software Services Ltd | Information & communication | 2021 |
| Mars Sun Technolgies Ltd | Information & communication | 2026 |
| Marshmoor Ltd | Construction | 2025 |
| Marsillac Associates Limited | Real estate | 2002 |
| Martin's Carpet Cleaning Company Limited | Administrative & support | 2010 |
| Martskazco Ltd. | Professional & scientific | 2010 |
| Maruti Soft Solutions Ltd | Information & communication | 2026 |
| Marvellous Trading Limited | Extraterritorial | 2015 |
| Mastercorp Ltd | Administrative & support | 2022 |
| Masti Events Limited | Arts & recreation | 2023 |
| Maurice Anthony Limited | Wholesale & retail | 1977 |
| Mavi Catering Limited | Hospitality | 2024 |
| Maxson Properties Ltd | Real estate | 2020 |
| MAY Day Books Limited | Professional & scientific | 2018 |
| Mayatza Consulting Ltd | Professional & scientific | 2016 |
| Mayhall Farm Residents Ltd | Households | 2000 |
| Mayley Investments Ltd | Real estate | 2025 |
| Mayo Brothers Ltd | Wholesale & retail | 2018 |
| MB Barber Lounge Limited | Other services | 2024 |
| MBM Appliances Ltd | Wholesale & retail | 2017 |
| Mbwl International Limited | Administrative & support | 2017 |
| MC Squared Business Management Limited | Wholesale & retail | 2019 |
| Mccoll Design Limited | Arts & recreation | 1962 |
| Mcnee Imaging Ltd | Health & social care | 2026 |
| Mcps Corporate Trustee Limited | Professional & scientific | 2023 |
| MDA Paradressage Limited | Arts & recreation | 2025 |
| MDH01 Ltd | Financial services | 2023 |
| Meadowbridge Holdings Limited | Professional & scientific | 1975 |
| Medallion Pharma Ltd | Health & social care | 2024 |
| Medi-Plant Engineering Services Limited | Professional & scientific | 1988 |
| Media Education Association | Education | 2006 |
| Mediamap Consulting Ltd | Professional & scientific | 2016 |
| Medic Line Auto Sales Ltd | Wholesale & retail | 2021 |
| Medical Creatives Ltd | Professional & scientific | 2020 |
| Medical Transportation Specialists Ltd | Transport & logistics | 2017 |
| Mehaj Enterprises Ltd | Real estate | 2016 |
| Meilin Ltd | Hospitality | 2026 |
| Melford Electronics Limited | Extraterritorial | 2014 |
| Melford Technologies Limited | Manufacturing | 2014 |
| Melon Street Property Ltd | Real estate | 2025 |
| Mema Construction & Electrics Ltd | Construction | 2019 |
| Memory Spot Limited | Wholesale & retail | 2000 |
| Mental Health Unit - Media Ltd | Information & communication | 2024 |
| Mentor Mums C.I.C. | Other services | 2021 |
| Mercado-Graham Ltd | Professional & scientific | 2026 |
| Merson Palmer Executive Search Limited | Administrative & support | 2008 |
| Metabun Ltd | Information & communication | 2022 |
| Metadata Technologies Limited | Information & communication | 2012 |
| Metals Unlimited Ltd | Wholesale & retail | 2010 |