| Montague Asset Management LLP | | 2012 |
| Monte Art Limited | Wholesale & retail | 2021 |
| Montgomery Gidney Limited | Construction | 2004 |
| Monumart Limited | Wholesale & retail | 2014 |
| Monument Avenue Ltd | Real estate | 2017 |
| Monument Mortgages Limited | Financial services | 2022 |
| Monument Park Ltd | Real estate | 2017 |
| Moon & Mushroom Ltd. | Hospitality | 2012 |
| Mooncalf Mercantile Ltd | Wholesale & retail | 2024 |
| Moonlight Guidance Ltd | Other services | 2019 |
| Moonraker Innovation Ltd | Professional & scientific | 2022 |
| Moore Artist Management Ltd | Arts & recreation | 2025 |
| Moore Brickwork Ltd | Construction | 2025 |
| Moore FOX Limited | Arts & recreation | 2013 |
| Moose on the Hill Limited | Wholesale & retail | 2022 |
| Moose Padel Limited | Wholesale & retail | 2026 |
| Mor'Manik Ltd | Wholesale & retail | 2011 |
| Mor-Properties Ltd | Real estate | 2022 |
| Mor-Tech Computing Services Ltd | Information & communication | 2017 |
| Mora Enterprises Ltd | Hospitality | 2018 |
| Moraru Transport Limited | Transport & logistics | 2018 |
| More Transport Limited | Transport & logistics | 2021 |
| Morecambe Bay Construction Ltd | Construction | 2021 |
| Morefield Engineering Limited | Other services | 2022 |
| Moreira Quality Used Cars Ltd | Other services | 2012 |
| Morello Estates Ltd | Real estate | 2024 |
| Morgan Group Ltd | Other services | 2015 |
| Morgan Law (Financial Services) Limited | Financial services | 1992 |
| Morlaix Project Management Ltd | Professional & scientific | 2012 |
| Morling Property Ltd | Real estate | 2025 |
| Morning DEW Service Ltd | Education | 2017 |
| Morning Star Transport Ltd | Transport & logistics | 2024 |
| Moroz Limited | Transport & logistics | 2020 |
| Morph Utilities Ltd | Construction | 2022 |
| Morrison Freight Holdings Limited | Financial services | 2004 |
| Morrison Freight Limited | Transport & logistics | 1989 |
| Morrison Group Limited | Financial services | 2015 |
| Morton Smith & Girling Ltd | Real estate | 2011 |
| Mosa Haulage Ltd | Transport & logistics | 2024 |
| Moss Family Office Ltd | Financial services | 2023 |
| Mossreal Consultancy Ltd | Professional & scientific | 2018 |
| Mostcommercials Ltd | Information & communication | 2025 |
| Motara Lifestyle Ltd | Wholesale & retail | 2022 |
| Moth Bar Ltd | Hospitality | 2020 |
| Motion Components Ltd | Wholesale & retail | 2003 |
| Motion Mapping Ltd | Information & communication | 2015 |
| Motion Watches UK Ltd | Wholesale & retail | 2017 |
| Motionwave Ltd | Information & communication | 2024 |
| Motivation Matters Limited | Administrative & support | 2004 |
| Moto 39 Group Ltd | Wholesale & retail | 2024 |
| Moto Torque Hub Limited | Wholesale & retail | 2025 |
| Motokind Ltd | Wholesale & retail | 2025 |
| Mould Plas Ltd | Manufacturing | 2018 |
| Mould Zero Ltd | Construction | 2025 |
| Mounalian Ltd | Health & social care | 2025 |
| Mount Cash & Carry Ltd | Wholesale & retail | 2022 |
| Mount Leopold Ltd | Professional & scientific | 2022 |
| Mount Place Management Company Limited | Households | 2019 |
| Mount Pleasant Management Company (Ilkley) Limited | Households | 1995 |
| Mountain Bike Coaching UK T/A (MBC UK) Ltd | Arts & recreation | 2011 |
| Mountain View Wealth Ltd | Administrative & support | 2020 |
| Mountbatten Estates Limited | Real estate | 2021 |
| Mountbatten Living Limited | Real estate | 2021 |
| Mountjoy Eleven Ltd | Real estate | 2016 |
| Mouse on Cheese Ltd | Wholesale & retail | 2022 |
| Mousesale Properties Ltd | Real estate | 2010 |
| Movers and Shakers Mobile Bars Limited | Hospitality | 2023 |
| Moving on Forward Ltd | Education | 2014 |
| Movingcare Agency Ltd | Health & social care | 2021 |
| Moxii Ltd | Wholesale & retail | 2025 |
| Moxon Technical Limited | Information & communication | 2025 |
| Moyes Place Management Company Ltd | Real estate | 2019 |
| Moyfish Limited | Professional & scientific | 2020 |
| Moyo Anima Limited | Information & communication | 2026 |
| Moyou Marketing Ltd | Wholesale & retail | 2011 |
| MOZ Engineering Services Ltd | Manufacturing | 2024 |
| Mo’S Toes Limited | Health & social care | 2025 |
| MP & Partners Veterinaria Limited | Professional & scientific | 2021 |
| MP Electrical Services Limited | Construction | 2005 |
| Mp's Massages Ltd | Other services | 2023 |
| MPF by Marco Limited | Administrative & support | 2025 |
| Mpjr Property Ltd | Real estate | 2025 |
| MPM Speed Limited | Transport & logistics | 2025 |
| MPS Energy Limited | Professional & scientific | 2016 |
| MPX Global Ltd | Construction | 2018 |
| MR and MRS Jones Music Ltd | Information & communication | 2025 |
| MR Barbu Ltd | Transport & logistics | 2021 |
| MR Misty Limited | Construction | 2013 |
| MR Painting and Decorating Ltd | Construction | 2024 |
| MR T Barber Ltd | Other services | 2025 |
| MRA Ipswich Ltd | Hospitality | 2026 |
| MRC Building Services Ltd | Construction | 2021 |
| MRM Holdings (EA) Limited | Financial services | 2012 |
| MRM Technical Services Limited | Other services | 1990 |
| MRP Technologies Ltd | Information & communication | 2025 |
| MS Beton Ltd | Construction | 2024 |
| MS Konsulting Circle Ltd | Information & communication | 2017 |
| MS Noble Group Ltd | Wholesale & retail | 2025 |
| MS One Build Ltd | Construction | 2025 |
| MS Quick Service Limited | Transport & logistics | 2021 |