| LYN Vaughan Ltd | Real estate | 2025 |
| Lynch Planning Consultancy Limited | Professional & scientific | 2006 |
| Lyncroft Ltd | Real estate | 2020 |
| Lynx BUS & Coach Transport Solutions Limited | Transport & logistics | 2025 |
| Lyons Distribution Limited | Transport & logistics | 2014 |
| Lyttle Communications Ltd | Professional & scientific | 2018 |
| M C Carpentry Limited | Construction | 2002 |
| M L G Consultants Limited | Professional & scientific | 2020 |
| M Slater Property Services Limited | Construction | 2023 |
| M W Construction (South) Limited | Other services | 2017 |
| M Wilson Builders Limited | Construction | 2019 |
| M&T Ltd | Financial services | 2017 |
| M.C.S. Management Services Limited | Professional & scientific | 2001 |
| M.H. & Sons Ltd | Arts & recreation | 2009 |
| Macar Bespoke (Kingswood) Limited | Construction | 2023 |
| Macar Bespoke (Ronmar) Limited | Construction | 2022 |
| Macar Bespoke (SA) Limited | Construction | 2023 |
| Macar Bespoke (WHL) Limited | Construction | 2022 |
| Macar Bespoke Limited | Construction | 2022 |
| Macar Developments (24CCR) Limited | Construction | 2020 |
| Macar Developments (352CVR) Limited | Construction | 2020 |
| Macar Developments (41WVR) Limited | Real estate | 2017 |
| Macar Developments (Park Road) Limited | Construction | 2023 |
| Macar Developments (TG) Limited | Construction | 2022 |
| Macar Homes (BC) Limited | Construction | 2024 |
| Macar Homes (Hoddesdon) Limited | Construction | 2026 |
| Macar Homes (Horsted Keynes) Limited | Construction | 2025 |
| Macar Homes (Northern Home Counties) Limited | Construction | 2022 |
| Macar Homes (Rustington) Limited | Construction | 2025 |
| Macar Homes (Southern Home Counties) Limited | Construction | 2017 |
| Macar Land Limited | Construction | 2022 |
| Macar Living (Bramley Hill) Limited | Construction | 2022 |
| Macar Living (City House) Limited | Construction | 2022 |
| Macar Living Limited | Construction | 2022 |
| Macar Partnerships (QVH) Limited | Construction | 2024 |
| Macar Partnerships (Ringmer) Limited | Construction | 2024 |
| Macar Property Group Limited | Financial services | 2022 |
| MACH8ZERO (Risk) Limited | Financial services | 2024 |
| MAD JAK Limited | Wholesale & retail | 1976 |
| Madd Creative Ltd | Extraterritorial | 2022 |
| Maddisons Barbers Limited | Other services | 2020 |
| Made Architects Limited | Professional & scientific | 2022 |
| Magnacorp Building Solutions Ltd | Professional & scientific | 2012 |
| Magnolia Property Management Limited | Real estate | 2017 |
| Maguire Care Limited | Health & social care | 2022 |
| Mainline Construction Limited | Construction | 1997 |
| Maison DU Velo Limited | Wholesale & retail | 2013 |
| Maja Mining Limited | Professional & scientific | 2013 |
| Maja Residential Limited | Real estate | 2016 |
| Major Players Racing Limited | | 1993 |
| Make IT Stick Consulting Ltd | Professional & scientific | 2018 |
| Making Good Limited | Wholesale & retail | 2010 |
| Malcolm Pawley Architects Limited | Professional & scientific | 2008 |
| Malmstone Ltd | Administrative & support | 2023 |
| MAN & MAN Ltd | Real estate | 2001 |
| MAN About a Dog Studio Limited | Arts & recreation | 2007 |
| Mandene Shop Ltd | Other services | 2024 |
| Manoeuvre Management Limited | Professional & scientific | 2014 |
| Manor Construction & Management Services Limited | Construction | 1996 |
| Manu Forti Capital Ltd | Construction | 2023 |
| Maple CM Limited | Health & social care | 2015 |
| Maplebright LLP | | 2012 |
| Mapleserve Limited | Information & communication | 2003 |
| Maplewood UK Developments Ltd | Construction | 2016 |
| Marcia Murphy Limited | Professional & scientific | 2014 |
| Marcin Kowalski IT Consulting Ltd | Information & communication | 2018 |
| Marcus Knightley Technical Limited | Construction | 1999 |
| Marellan Ltd | Construction | 2015 |
| Margalla Ltd | Health & social care | 2024 |
| Mark Carden Associates Limited | Professional & scientific | 2009 |
| Mark Edwards Consulting Limited | Professional & scientific | 2011 |
| Marked Audio Limited | Information & communication | 2026 |
| Marketing & Management International Limited | Arts & recreation | 1986 |
| Marpeg Ltd | Wholesale & retail | 2016 |
| Marsden Education Limited | Education | 2025 |
| Marshall Clark (Crawley) LLP | | 2006 |
| Marshglobe Limited | Real estate | 1993 |
| Marthams Holdings Limited | Other services | 2021 |
| Martin Drew Limited | Professional & scientific | 2019 |
| Martineaux Electrical Services Limited | Construction | 2010 |
| Martins Maintenance, Decorating and Repairs Ltd | Administrative & support | 2021 |
| Maru Consulting Ltd | Professional & scientific | 2021 |
| Masterpiece Engineering Limited | Manufacturing | 2015 |
| Masworth Properties Limited | Extraterritorial | 2020 |
| Matalex Property Services Limited | Financial services | 2025 |
| Matrix Advice Ltd | Professional & scientific | 2002 |
| Matrix Management Group Limited | Real estate | 2024 |
| Matt Cull Consulting Ltd | Professional & scientific | 2018 |
| Matt Spencer Limited | Professional & scientific | 2011 |
| Matt Swain Ltd | Professional & scientific | 2021 |
| Matthew James Properties Limited | Construction | 2024 |
| Matts Home Services Limited | Other services | 2008 |
| MAX Cloud Services Limited | Information & communication | 2019 |
| Maxco London Limited | Administrative & support | 2015 |
| Maxfield Kadlubowski Developments Limited | Real estate | 2005 |
| Maxfield Kadlubowski Group Limited | Wholesale & retail | 2001 |
| Maxwell Valentine Limited | Real estate | 2009 |
| Mayfair & Kensington Property Management Limited | Real estate | 2014 |
| Mayford People Solutions Limited | Professional & scientific | 2023 |
| Mayki Ltd | Extraterritorial | 2013 |