| Mary's Munch Cafe Ltd | Hospitality | 2017 |
| Maryfield Ltd | Real estate | 2020 |
| Maryjo Properties Limited | Real estate | 2002 |
| Maryland Trust Company (Leeds) Limited | Professional & scientific | 1969 |
| Marylebone (MM) Limited | Real estate | 2020 |
| Marymap Community Care Limited | Administrative & support | 2017 |
| Marz & Mars Services Limited | Real estate | 2023 |
| MAS Bake Co. Ltd | Hospitality | 2026 |
| MAS Clearance Leeds Limited | Transport & logistics | 2025 |
| MAS D&R Ltd | Transport & logistics | 2025 |
| MAS Design Consultants Limited | Professional & scientific | 2001 |
| MAS O Menos Ltd | Construction | 2022 |
| MAS Orthotics Ltd | Health & social care | 2025 |
| MAS Properties Limited | Real estate | 2019 |
| Masa Maritime Ltd | Transport & logistics | 2023 |
| Masa Team Limited | Information & communication | 2022 |
| Masala HUT Crossgates Ltd | Hospitality | 2026 |
| Masana Consulting Services Ltd | Information & communication | 2006 |
| Masana Properties Ltd | Real estate | 2017 |
| Masato Limited | Manufacturing | 2012 |
| Masco Corporation Limited | Professional & scientific | 1985 |
| Masella Entertainment Ltd | Arts & recreation | 2025 |
| Mash Marketing Consultancy Ltd | Professional & scientific | 2023 |
| Mashaco Helping Hands Care Ltd | Health & social care | 2021 |
| Masham Court Limited | Households | 1982 |
| Mashaz Ltd | Wholesale & retail | 2021 |
| Mashipi Logistics Ltd | Transport & logistics | 2025 |
| Mashup Media Marketing Ltd | Professional & scientific | 2015 |
| Mashy's Investments Ltd | Real estate | 2021 |
| Masi Care Limited | Other services | 2020 |
| Masi Consulting Limited | Information & communication | 2022 |
| Masihe Ltd | Wholesale & retail | 2026 |
| Maskill Construction Ltd | Construction | 2024 |
| Maskill Estates Limited | Professional & scientific | 2024 |
| Masokana Ltd | Health & social care | 2026 |
| Masombuka Health Care Limited | Health & social care | 2026 |
| Mason & Co Ltd | Hospitality | 2000 |
| Mason Agri Seeds Limited | Wholesale & retail | 2023 |
| Mason Harding Ltd | Administrative & support | 2022 |
| Mason Motors Limited | Wholesale & retail | 2018 |
| Mason Properties Empire Limited | Real estate | 2023 |
| Mason Stuart Homes Limited | Construction | 2012 |
| Mason Technologies Limited | Information & communication | 1998 |
| Mason Townsend Limited | Administrative & support | 2024 |
| Mason-Fieldhouse Investments Ltd | Financial services | 2025 |
| Masonsofts Limited | Information & communication | 2026 |
| Masontone Limited | Hospitality | 1985 |
| Masonwood Construction Ltd | Construction | 2021 |
| Masood Butchers Ltd | Wholesale & retail | 2020 |
| Masowa Ltd | Transport & logistics | 2015 |
| Maspinall IT Ltd | Information & communication | 2023 |
| Masq Ltd | Administrative & support | 2018 |
| Mass Enterprise Ltd | Transport & logistics | 2014 |
| Mass Housing Limited | Real estate | 2019 |
| Mass Media Outdoor Limited | Professional & scientific | 2020 |
| Massage Andreea Limited | Health & social care | 2025 |
| Massage Point Centre Ltd | Other services | 2026 |
| Masschart Limited | Real estate | 1987 |
| Massive (UK) Group Limited | Financial services | 2022 |
| Massive (UK) Ltd | Other services | 2013 |
| Massive Event Services (UK) Limited | Other services | 2020 |
| Massive Research & Insight Limited | Administrative & support | 2025 |
| Mast Power Services Limited | Professional & scientific | 2025 |
| Mast Solar Ltd | Construction | 2025 |
| Master and Co Leeds Limited | Wholesale & retail | 2020 |
| Master Barber 109 Ltd | Other services | 2026 |
| Master Barber Otley Ltd | Other services | 2025 |
| Master Cash & Carry Limited | Wholesale & retail | 2021 |
| Master Consultancy & Management Limited | Professional & scientific | 2020 |
| Master Couriers Limited | Transport & logistics | 2019 |
| Master Print & Signs (National) Ltd | Hospitality | 2015 |
| Master Special Burger Limited | Hospitality | 2026 |
| Master Tailor Limited | Wholesale & retail | 1991 |
| Master Your Future Ltd | Information & communication | 2022 |
| Mastercoat Northern Ltd | Construction | 2025 |
| Mastercraft Property Developments Ltd | Construction | 2018 |
| Masterminds Solutions Limited | Wholesale & retail | 2023 |
| Masternaut Group Holdings Limited | Information & communication | 2009 |
| Masternaut Holdings Limited | Information & communication | 2001 |
| Masternaut Limited | Information & communication | 2011 |
| Masternaut Risk Solutions Limited | Information & communication | 2011 |
| Masters Analytics Ltd | Information & communication | 2014 |
| Masters of Scissors Ltd | Other services | 2021 |
| Mastery Apps Ltd | Information & communication | 2023 |
| Masuria Properties Ltd | Real estate | 2016 |
| MAT Elec Ltd | Construction | 2024 |
| MAT Fitness Limited | Arts & recreation | 2026 |
| MAT Foods Barnsley Ltd | Hospitality | 2024 |
| MAT Private Hire Ltd Ltd | Administrative & support | 2026 |
| Mat-Tech IT Consulting Limited | Information & communication | 2026 |
| Matalex Ltd | Transport & logistics | 2021 |
| Matb Asset Holdings Ltd | Financial services | 2026 |
| Matb Estates Ltd | Real estate | 2026 |
| Matb Properties Ltd | Real estate | 2026 |
| Matcha Melon Ltd | Wholesale & retail | 2025 |
| Matchacafe Ltd | Hospitality | 2025 |
| Matchbox Solutions Ltd | Information & communication | 2018 |
| Matchestalent Ltd | Administrative & support | 2018 |
| Matchfit Consults Limited | Professional & scientific | 2022 |
| Material Matters Studio Ltd | Construction | 2026 |