| Morse Security Consulting Limited | Administrative & support | 2024 |
| Mortgage Steps Limited | Financial services | 2004 |
| Mortgage Today (East Anglia) Limited | Financial services | 2017 |
| MORTGAGE321 Limited | Administrative & support | 2011 |
| Mortgages 4 Retirement Ltd | Financial services | 2022 |
| Mortgages Direct Limited | Administrative & support | 1993 |
| Mortgages First Ltd | Financial services | 2006 |
| Mortgages for Actors Ltd | Financial services | 2019 |
| Mortimer Court (Colchester) Management Company Limited | Households | 2007 |
| Morton Climate Ltd | Construction | 2026 |
| Morton Hiab Ltd | Transport & logistics | 2013 |
| MOS Plumbing and Heating Services Ltd | Construction | 2021 |
| Mosaic Foster Care (Holdings) Limited | Financial services | 2020 |
| Mosaic Publicity Limited | Administrative & support | 2000 |
| Mosaje Ltd | Wholesale & retail | 2019 |
| Mosambik Limited | Administrative & support | 2019 |
| Moseyno Digital Limited | Information & communication | 2021 |
| Mosley& Limited | Professional & scientific | 2010 |
| Moss Bros Roofing Limited | Construction | 2024 |
| Moss Craft London Ltd | Wholesale & retail | 2025 |
| Motara Marine Ltd. | Information & communication | 2016 |
| Moth House Studio Limited | Professional & scientific | 2025 |
| Moth Works Ltd | Real estate | 2022 |
| Mother's Care and Support Ltd | Health & social care | 2024 |
| Motherland African Market Ltd | Wholesale & retail | 2025 |
| Motion Dance Academy Essex LLP | | 2024 |
| Motion New Media Limited | Information & communication | 2001 |
| Motiv Plus Ltd | Real estate | 2020 |
| Motivatia Limited | Information & communication | 2003 |
| Motor Schools Association of Great Britain Limited(The) | Other services | 1958 |
| Motorbike Warehouse Limited | Transport & logistics | 2001 |
| Motorfarm Ltd | Wholesale & retail | 2025 |
| Motorwise Limited | Wholesale & retail | 2013 |
| Motts Body Repair Limited | Wholesale & retail | 2005 |
| Moulsham Lodge Management Company Limited | Households | 2018 |
| Moulsham Residential Home (Chelmsford) Limited | Health & social care | 2000 |
| Mount Services Limited | Wholesale & retail | 2019 |
| Mountague Properties Limited | Real estate | 2021 |
| Mountair Limited | Manufacturing | 2008 |
| Mouri Smart Ltd | Hospitality | 2017 |
| Mourpotential Ltd | Professional & scientific | 2011 |
| Mouse Holdings Limited | Administrative & support | 2012 |
| Move Plus (South East) Limited | Real estate | 2022 |
| Movewell Health Limited | Health & social care | 2026 |
| MOW 'N' Go Ltd | Administrative & support | 2025 |
| Moye Property Holdings Limited | Financial services | 2022 |
| Moyes Financial Planning Limited | Financial services | 2011 |
| Moyes Investments International Ltd | Financial services | 2026 |
| Moyesii Ltd | Manufacturing | 2022 |
| MP &OAS Ltd | Health & social care | 2019 |
| MP Digital Solutions Ltd | Information & communication | 2025 |
| MP Energy Consultants Limited | Administrative & support | 2016 |
| MP Fibre Ltd | Professional & scientific | 2018 |
| MP Gallery Limited | Wholesale & retail | 2017 |
| MP Properties Management Ltd | Real estate | 2024 |
| MP Property Solutions Ltd | Real estate | 2013 |
| Mpak Advisory Limited | Professional & scientific | 2020 |
| Mpelectricians Ltd | Construction | 2020 |
| MPL Claims Management Ltd | Administrative & support | 2018 |
| MPL Legal Services Ltd | Professional & scientific | 2023 |
| MPL Structural Engineering Ltd | Professional & scientific | 2024 |
| MPM Trade Ltd | Construction | 2020 |
| MPS Vehicle Refinishers Limited | Wholesale & retail | 2007 |
| Mpume’S Limited Limited | Public administration | 2026 |
| MR Accommodation Ltd | Real estate | 2024 |
| MR Boiler Services Ltd | Construction | 2003 |
| MR Engineering Consulting Services Ltd | Construction | 2016 |
| MR Home Improvements (Essex) Limited | Construction | 2011 |
| MR Lamb Maths Ltd | Education | 2025 |
| MR O Estate Agents Ltd | Real estate | 2023 |
| MR Phone Exchange Ltd | Wholesale & retail | 2015 |
| MR Porter Construction Ltd | Construction | 2023 |
| MR Props Ltd | Professional & scientific | 2018 |
| MR SAM FIX IT Ltd | Other services | 2024 |
| MR Suds Limited | Administrative & support | 2018 |
| MR T Joinery & Building Ltd. | Construction | 2014 |
| MR Zafar Maan Ltd | Health & social care | 2015 |
| MR. Mastic Limited | Construction | 1997 |
| MRB Construction Services Limited | Construction | 2015 |
| MRC Holiday Homes Ltd | Hospitality | 2022 |
| MRC Sourcing Ltd | Wholesale & retail | 2011 |
| MRF Firm Limited | Information & communication | 2025 |
| Mrme Solutions Ltd | Professional & scientific | 2024 |
| MRO Africa Limited | Professional & scientific | 2014 |
| MRR Rice Brand Ltd | Wholesale & retail | 2025 |
| MRS Busy Bees Limited | Households | 2016 |
| MRS Roots Gardens Limited | Administrative & support | 2022 |
| Mrsc Limited | Other services | 2012 |
| MRT Protection Services Limited | Administrative & support | 2015 |
| MS Lifting Solutions Ltd | Construction | 2017 |
| MS Loyal Mart Ltd | Wholesale & retail | 2025 |
| MS Temple Limited | Professional & scientific | 2018 |
| MS5 Projects Limited | Professional & scientific | 2025 |
| MSA Cornelius Limited | Transport & logistics | 2026 |
| Msbs Properties Limited | Real estate | 2022 |
| Msfp Consulting and Investment Limited | Professional & scientific | 2013 |
| MSN Build Limited | Construction | 2011 |
| MSR Capital Investments Ltd | Wholesale & retail | 2025 |
| MSR Medical Ltd | Education | 2018 |
| MSR Store Limited | Manufacturing | 2018 |