| LTR Property Group Ltd | Real estate | 2021 |
| LTY Holdings Ltd | Households | 2024 |
| Lucid Development Limited | Information & communication | 2021 |
| Lucky 88 Takeaway Limited | Hospitality | 2025 |
| Lukat Ltd | Manufacturing | 2023 |
| Luke Sayer Engineering Ltd | Professional & scientific | 2020 |
| Luna Capital Group Holdings Limited | Real estate | 2020 |
| Luna Capital Group LLP | | 2020 |
| Luna Wolfe Ltd | Manufacturing | 2023 |
| Lunt Residential Ltd | Real estate | 2025 |
| Lunt Solutions Ltd | Information & communication | 2025 |
| Lwin Family Holdings Ltd | Real estate | 2019 |
| Lwin Family Partnership LLP | | 2019 |
| Lygo Joinery Company Limited | Construction | 2024 |
| Lynch Family Partnership LLP | | 2019 |
| Lyon Family Holdings Ltd | Real estate | 2017 |
| Lyon Family Partnership LLP | | 2017 |
| M & a Patel WP Ltd | Administrative & support | 2024 |
| M & D Travel Limited | Transport & logistics | 2011 |
| M & D Wilson WP Ltd | Professional & scientific | 2024 |
| M & L Mitchell WP Ltd | Administrative & support | 2024 |
| M & M Residential Partnership LLP | | 2017 |
| M & P Mcnicholas Ltd | Real estate | 2021 |
| M & V Lewis WP Ltd | Administrative & support | 2024 |
| M & V Locum Services Ltd | Health & social care | 2019 |
| M Culley Window Repairs Ltd | Construction | 2025 |
| M Deans WP Ltd | Administrative & support | 2024 |
| M E Leisure Limited | Hospitality | 2003 |
| M Erguven WP Ltd | Professional & scientific | 2024 |
| M S Vehicle Repairs Ltd | Professional & scientific | 2026 |
| M Shaunak Holdings Limited | Real estate | 2019 |
| M Stone WP Ltd | Administrative & support | 2024 |
| M Wrench Property Services Limited | Real estate | 2006 |
| M&C DE Friend WP Ltd | Administrative & support | 2024 |
| M&M Residential Holdings Ltd | Real estate | 2017 |
| M&S Lettings Partnership LLP | | 2022 |
| M&Z Medical Group Ltd | Health & social care | 2025 |
| M. Shawgi Ltd | Health & social care | 2018 |
| M.A.C Roofing & SON Ltd | Construction | 2018 |
| M.D. (Billingham) Limited | Construction | 2009 |
| M2 Environmental Limited | Professional & scientific | 2011 |
| M3 Broadway Limited | Real estate | 2003 |
| M36B LLP | | 2020 |
| M3S Properties Ltd | Real estate | 2022 |
| Maakuf Family Partnership LLP | | 2021 |
| Maakuf Ltd | Real estate | 2020 |
| Macade Finance Limited | Professional & scientific | 2002 |
| Macaskill Management Limited | Real estate | 2017 |
| Maccombe Family Holdings Limited | Real estate | 2020 |
| Maccombe Family Partnership LLP | | 2020 |
| Mach Leasing Ltd | Real estate | 2020 |
| Mackenzie Motorhomes Ltd | Administrative & support | 2025 |
| Macleods Pharma UK Limited | Manufacturing | 2007 |
| Madcock Ltd | Real estate | 2018 |
| Maddison Family Partnership LLP | | 2016 |
| Maddison Plumbing Heating and GAS Services Limited | Construction | 2002 |
| Madeira Group Holdings Ltd | Real estate | 2021 |
| Madeira Group Partnership LLP | | 2021 |
| Madhok Family Holdings Ltd | Real estate | 2018 |
| Madhok Family Partnership LLP | | 2018 |
| Maffs Gardening Services Ltd | Administrative & support | 2022 |
| Magnazen Ltd | Administrative & support | 2018 |
| Magnum Holdings UK Limited | Wholesale & retail | 2009 |
| Magnum Investments (NE) Limited | Real estate | 2018 |
| Magnum Packaging (N.E.) Limited | Wholesale & retail | 1983 |
| Magnum Packaging Limited | Wholesale & retail | 2009 |
| Magnum Storage (NE) Limited | Transport & logistics | 2010 |
| Magnum Storage Limited | Transport & logistics | 2015 |
| Magpie Hedgeco Limited | Financial services | 2023 |
| Magpie Holdco Limited | Financial services | 2023 |
| Magpie Investco Limited | Financial services | 2023 |
| Magpie Midco 1 Limited | Financial services | 2023 |
| Magpie Midco 2 Limited | Financial services | 2023 |
| Magpie UK Bidco Limited | Financial services | 2023 |
| Mahmoud Khashashneh Ltd | Health & social care | 2025 |
| Mahoney Finance Group Ltd | Administrative & support | 2021 |
| Maid in Teesside Ltd | Administrative & support | 2019 |
| Maidenhead Lettings Limited | Real estate | 1997 |
| Make & Mend Company Limited | Arts & recreation | 2018 |
| Maksafe Electrical & Site Services Ltd | Manufacturing | 2022 |
| MAL Distribution Ltd | Wholesale & retail | 2025 |
| Mandurah Limited | Hospitality | 2022 |
| Manley Summers Limited | Administrative & support | 1985 |
| Manorside Construction Ltd | Manufacturing | 2020 |
| Manup Access Ltd | Construction | 2015 |
| Manzil Properties Limited | Real estate | 2007 |
| Maps Engineering Limited | Professional & scientific | 2020 |
| Marcorios - TI Parthenos Ltd | Health & social care | 2023 |
| Marine BIO Services Ltd | Water & waste | 2013 |
| Marine Safety Technologies Limited | Professional & scientific | 2020 |
| Mark Brogan Family Holdings Limited | Real estate | 2018 |
| Marmaris Barber (NE) Limited | Other services | 2023 |
| Martin Cattermole Plumbing & Heating Ltd | Water & waste | 2015 |
| Marvellous Minifigures Limited | Wholesale & retail | 2020 |
| Marwood Comms Limited | Information & communication | 2026 |
| Mascari Family Holdings Limited | Real estate | 2018 |
| Mascari Family Partnership LLP | | 2019 |
| Matildas Prep Kitchen Ltd | Hospitality | 2025 |
| Matrix Couriers Ltd | Transport & logistics | 2025 |
| Matthew Towers Services Ltd | Professional & scientific | 2019 |