| LOW Life Lifestyle Ltd | Wholesale & retail | 2025 |
| Lunar Incorporated Limited | Administrative & support | 2019 |
| Lunch Whistle Ltd | Other services | 2025 |
| Lustig & Webb Limited | Other services | 2014 |
| Lustig & Webb Storrington Limited | Other services | 2023 |
| Luxury Bathrooms & Kitchens Ltd | Construction | 2023 |
| Lz-Uk Ltd | Professional & scientific | 2021 |
| M City Cars Ltd | Wholesale & retail | 2016 |
| M&C Inns Ltd | Hospitality | 2022 |
| M&G Productions Ltd | Professional & scientific | 2017 |
| M.A.P. Audio Visual Limited | Information & communication | 2013 |
| M.B.H. (Remedial) Ltd | Real estate | 1998 |
| M.G.I. Properties Limited | Other services | 1995 |
| M4-ANG Ltd | Administrative & support | 2017 |
| M7BCONSULTANCY Ltd | Education | 2025 |
| Mabb Holdings Ltd | Real estate | 2025 |
| Mach Schau Limited | Professional & scientific | 2012 |
| Mach Schau Studios Ltd | Financial services | 2024 |
| Machan Limited | Real estate | 2009 |
| Mackenzie Ford Limited | Professional & scientific | 2000 |
| Mactok Ltd | Administrative & support | 2025 |
| MAD Designs Limited | Real estate | 2021 |
| Madcal Holdings Limited | Financial services | 2026 |
| Madeleine Jean Ltd | Wholesale & retail | 2021 |
| Mafilip Ltd | Health & social care | 2010 |
| Magnetic Moon Coaching Ltd | Administrative & support | 2020 |
| MAIDS2GO Ltd | Administrative & support | 2021 |
| Majic EYE Productions Ltd | Information & communication | 2024 |
| Mall Research Consultancy Limited | Administrative & support | 2013 |
| MAN and BOY Film Limited | Information & communication | 2016 |
| Mandala Strategy Limited | Professional & scientific | 2025 |
| Manifest AI Ltd | Information & communication | 2024 |
| Manifest Films Limited | Information & communication | 2002 |
| Mapedeon Limited | Information & communication | 2025 |
| Maple Fifty Four Ltd | Information & communication | 2023 |
| Maple Leaf Community Planting CIC | Professional & scientific | 2025 |
| Marcus Grimes (Henfield) Limited | Real estate | 2016 |
| Mark King Media Ltd | Professional & scientific | 2025 |
| Marram Limited | Wholesale & retail | 2015 |
| Marshall Consultancy Limited | Professional & scientific | 2006 |
| Marshall Hamble Limited | Real estate | 2019 |
| MARTIC22 Ltd | Professional & scientific | 2022 |
| Martin Howlett Furniture Ltd | Manufacturing | 2024 |
| Martyr Construction Limited | Construction | 2019 |
| Martyr Developments Limited | Real estate | 2025 |
| Martyr Group Limited | Construction | 2025 |
| Mary Leslie Interior Design Ltd | Construction | 2002 |
| Mason & Tate Developments Limited | Real estate | 2017 |
| Mason & Tate Limited | Real estate | 2003 |
| Massive Media Group Limited | Information & communication | 2024 |
| Matcha Angels Ltd | Hospitality | 2026 |
| Matcm Ltd | Construction | 2025 |
| Matt Tatem Ltd | Information & communication | 2010 |
| Mattersoftheearth Ltd | Education | 2012 |
| Matthew Berryman Limited | Professional & scientific | 2014 |
| MAX ST John Projects Ltd. | Other services | 2015 |
| Maxfaxdentalimplants Limited | Health & social care | 2020 |
| Maximatic Limited | Other services | 1992 |
| Maxwell Harrington Ltd | Real estate | 2026 |
| MBM Structural Engineering Ltd | Professional & scientific | 2025 |
| MC Designers Group Limited | Construction | 1991 |
| Mccallum-Varey Limited | Information & communication | 1984 |
| MCD Heritage Limited | Construction | 2020 |
| MD Electrical Services Limited | Construction | 2004 |
| MD Group International Ltd | Administrative & support | 2015 |
| Meadow & Sweet Ltd | Hospitality | 2026 |
| Meadow View Park Limited | Hospitality | 2013 |
| Meadowall Group Ltd | Financial services | 2026 |
| Meadowfield Gardening Ltd | Administrative & support | 2025 |
| MED H20 Limited | Wholesale & retail | 2024 |
| Media Sound Limited | Information & communication | 1996 |
| Medigem Technology UK Limited | Real estate | 2015 |
| Meon Meadows Ltd | Agriculture & fishing | 2020 |
| Meridian Consulting and Advisory Services Limited | Administrative & support | 2025 |
| Meritun Limited | Health & social care | 2005 |
| Merlinet Limited | Information & communication | 2013 |
| Merrick Financial Services Ltd | Financial services | 2007 |
| Mesh Mash Limited | Arts & recreation | 2013 |
| Metaflo Limited | Information & communication | 2023 |
| Mexes Limited | Professional & scientific | 2014 |
| Mghm Investments Ltd | Real estate | 2025 |
| MGK Holdings Corporation Ltd | Financial services | 2026 |
| Mhoptix Ltd | Professional & scientific | 2018 |
| Miam London Limited | Administrative & support | 2021 |
| Michael a Baker Ltd | Manufacturing | 2016 |
| Michelangelo (Worthing) Limited | Hospitality | 2011 |
| MID Sussex Motors Limited | Wholesale & retail | 2012 |
| Mid-Sussex Golf Club Limited | Arts & recreation | 2010 |
| Middleton Estate Company Limited | Construction | 2006 |
| Mifa Smiles Ltd | Health & social care | 2024 |
| Mike Mulcahy Ltd | Health & social care | 2011 |
| Mike Southcombe Consultancy Limited | Professional & scientific | 2008 |
| Mikotta Ltd | Wholesale & retail | 2023 |
| Milepost Communications Limited | Professional & scientific | 2018 |
| Milton Residential Ltd | Real estate | 2025 |
| Mindful Cleans Ltd | Administrative & support | 2023 |
| Mkhalid Limited | Wholesale & retail | 2025 |
| ML Executives Limited | Administrative & support | 1991 |
| Mnkdevelopments Ltd | Construction | 2022 |
| MNS Oral Care Ltd | Health & social care | 2024 |