| Millennium Care Homes Limited | Administrative & support | 1995 |
| Millennium Consultancy Limited | Professional & scientific | 2016 |
| Millennium Corporation Ltd | Construction | 2022 |
| Millennium Dough Company Limited | Manufacturing | 1992 |
| Millennium Videographics Limited | Information & communication | 1998 |
| Millennium Wharf Freeholders Limited | Real estate | 2016 |
| Millennium Wharf Management Company Limited | Households | 1999 |
| Miller and Sons Accountants and Bookkeepers Ltd | Professional & scientific | 2019 |
| Miller Services Limited | Professional & scientific | 2015 |
| Millers Rise Management Company Limited | Households | 1988 |
| Millhaven Management Company Limited | Real estate | 1989 |
| Millicent Consulting Ltd | Professional & scientific | 2023 |
| Millow Properties Limited | Real estate | 2013 |
| Mills & Co Electrical Ltd | Construction | 2016 |
| Millstream Training Ltd | Health & social care | 2020 |
| Millwall Management Consulting Ltd | Professional & scientific | 2017 |
| Milo Trading Group Ltd | Wholesale & retail | 2024 |
| Milosh Group Limited | Construction | 2021 |
| Milsons Services Ltd | Construction | 2024 |
| Milukas Ltd | Construction | 2026 |
| Milvus Heights Properties Ltd | Households | 2025 |
| MIM Accountancy Ltd | Professional & scientific | 2021 |
| Mimco Limited | Hospitality | 2020 |
| Mimi Island Ltd | Other services | 2013 |
| Mimisho Ltd | Wholesale & retail | 2012 |
| Mind and Body Academy Ltd | Information & communication | 2021 |
| Mind First Group Limited | Education | 2021 |
| Mind in View LLP | | 2026 |
| Mind-Body-Fit Fitness Consultancy Limited | Arts & recreation | 2024 |
| Mindcode Ltd | Information & communication | 2024 |
| Mindful Property Solutions Ltd | Real estate | 2020 |
| Mindfulland Ltd | Education | 2023 |
| Minds Aligned Limited | Education | 2025 |
| Minds at WAR CIC | Information & communication | 2023 |
| Minds for Tomorrow CIC | Education | 2024 |
| Mindspring Health Limited | Health & social care | 2025 |
| Minerva Heights Management Company Limited | Households | 2004 |
| Minerva Production Entertainment Limited | Professional & scientific | 2024 |
| Minicab Accountants Ltd | Professional & scientific | 2018 |
| Miniemma Ltd | Real estate | 2020 |
| Minimo Smile Ltd | Health & social care | 2023 |
| Minney & Company Limited | Professional & scientific | 2013 |
| Minnow Enterprises Limited | Information & communication | 2004 |
| Minsec Ltd | Administrative & support | 2023 |
| Minsec Training Limited | Education | 2024 |
| Mint Haulage Ltd. | Transport & logistics | 2014 |
| Mintern Close (Management) Limited | Households | 1968 |
| Mintern Close Holding Limited | Households | 2005 |
| Minutia Skin Limited | Wholesale & retail | 2021 |
| MIP Builders Ltd | Construction | 2017 |
| Mipacts Limited | Professional & scientific | 2014 |
| Mirable Ltd | Wholesale & retail | 2025 |
| Mirabolis Ltd | Construction | 2016 |
| Miram 3 Limited | Construction | 2018 |
| Miram 6 Limited | Construction | 2018 |
| Miram House Management Limited | Real estate | 2015 |
| Mirani Products Limited | Wholesale & retail | 2025 |
| Mirat Associates Limited | Professional & scientific | 2024 |
| Mirco and SON Ltd | Construction | 2013 |
| Mire Jane Limited | Wholesale & retail | 2018 |
| Mirgi Ltd | Health & social care | 2023 |
| Miro Property Services Ltd. | Financial services | 2014 |
| Miron Services Ltd | Administrative & support | 2025 |
| Mirror Care Solutions Ltd | Health & social care | 2024 |
| Mirtex Group Ltd | Wholesale & retail | 2018 |
| Mirzan Ltd | Construction | 2023 |
| MIS Experts Limited | Information & communication | 2013 |
| Misbah Traders Ltd | Wholesale & retail | 2021 |
| Misha Dobrosevski Ltd | Other services | 2020 |
| Miska Consulting Ltd | Information & communication | 2025 |
| Mister Tacho Ltd | Professional & scientific | 2012 |
| Mister Urbane Limited | Wholesale & retail | 2020 |
| Mistify Ltd | Wholesale & retail | 2025 |
| Mistrytech Ltd | Information & communication | 2007 |
| Misty Buckley Design Ltd | Arts & recreation | 2010 |
| MIT Recyclers Limited | Wholesale & retail | 2012 |
| MIT Ventures 2 Ltd | Administrative & support | 2020 |
| MIT Ventures Limited | Administrative & support | 2018 |
| Mital Trading Limited | Wholesale & retail | 2010 |
| Mitchayl Limited | Arts & recreation | 2022 |
| Miterdale Limited | Information & communication | 2024 |
| Mitf Ltd | Information & communication | 2019 |
| Mitre Services Ltd | Administrative & support | 2015 |
| Mixam Associates Limited | Manufacturing | 2014 |
| Mixam UK Limited | Manufacturing | 2007 |
| Miyakam Ltd | Real estate | 2021 |
| MJ Ventures Ltd | Wholesale & retail | 2023 |
| MJ Visum Limited | Information & communication | 2019 |
| MJ Williams - Sky's the Limited | Real estate | 2012 |
| Mjali Consulting Ltd | Professional & scientific | 2023 |
| Mjdc Limited | Information & communication | 2011 |
| Mjjg Limited | Financial services | 2025 |
| MJK Finance Solutions Limited | Professional & scientific | 2020 |
| Mjlavoie Ltd | Information & communication | 2023 |
| Mjlsales Ltd | Transport & logistics | 2004 |
| MJR Consulting Services Ltd | Professional & scientific | 2018 |
| MJR Sutcliffe & Co Limited | Financial services | 2010 |
| MJS CAD Limited | Professional & scientific | 2026 |
| MJS Data Management Ltd | Professional & scientific | 2022 |
| MJS Packaging Services Ltd | Administrative & support | 2009 |