| Melisa Chikanda Limited | Other services | 2014 |
| Melissa Wheeler Consulting Ltd | Professional & scientific | 2025 |
| Melius Law Limited | Professional & scientific | 2023 |
| Melix Consulting Ltd | Professional & scientific | 2024 |
| Melle Tech Ltd | Information & communication | 2016 |
| Mello Care Services Ltd | Health & social care | 2026 |
| Melrose Agronomy Ltd | Agriculture & fishing | 2025 |
| Melrose Engineering Services Ltd | Professional & scientific | 2017 |
| Melrose Gardens Limited | Hospitality | 2024 |
| Melross AVE. Limited | Other services | 2018 |
| Melton Meadows Properties Ltd | Construction | 2018 |
| Mel’S Variety Store Ltd | Wholesale & retail | 2025 |
| Mensa Heating (UK) Limited | Wholesale & retail | 2019 |
| Mensima ENT Limited | Construction | 2026 |
| Mentality Art Ltd | Wholesale & retail | 2021 |
| Menterflow Limited | Real estate | 1986 |
| Mentorverse Ltd | Administrative & support | 2023 |
| Mentorway Limited | Education | 2025 |
| Menya Trans Ltd | Transport & logistics | 2024 |
| Meon Valley Builders Limited | Construction | 2011 |
| Meow Meow Seven Ltd | Real estate | 2018 |
| MEP Remote QS Ltd | Professional & scientific | 2022 |
| Mercantile London Ltd | Wholesale & retail | 2011 |
| Mercator International Limited | Professional & scientific | 2016 |
| Mercer-Co Ltd. | Information & communication | 2013 |
| Merchant Projects (Westerfield) Limited | Construction | 2009 |
| Merchrobot Ltd | Wholesale & retail | 2023 |
| Mercury Healthcare Limited | Health & social care | 2018 |
| Mercury Maynard Limited | Information & communication | 2015 |
| Meredith Building Company Ltd | Construction | 2002 |
| Mergebuild Ltd | Construction | 2025 |
| Merged Reality Ltd | Manufacturing | 2023 |
| Mergen IT Ltd | Information & communication | 2022 |
| Meriam Homes Limited | Real estate | 2022 |
| Meridian Hold Co Ltd | Financial services | 2020 |
| Meridian Invest Co Ltd | Real estate | 2020 |
| Meridian Private Healthcare Limited | Public administration | 2026 |
| Meridian Project Management Ltd | Professional & scientific | 2015 |
| Meridiana Consultancy Services Ltd | Information & communication | 2013 |
| Merit Asian Market Ltd | Hospitality | 2021 |
| Meritas Fire & Security Protection Limited | Administrative & support | 2016 |
| Merlin Classics Limited | Information & communication | 2004 |
| Merlin Cloud Ltd | Information & communication | 2023 |
| Merlin Pools & Spas LLP | | 2015 |
| Merlin Swimming Pools Limited | Construction | 2000 |
| Merrypebbles Ltd | Wholesale & retail | 2025 |
| Mersea Cars Limited | Wholesale & retail | 2014 |
| Mersea Estate Agency Limited | Professional & scientific | 1998 |
| Mersea Homes (Ipswich) Limited | Construction | 2008 |
| Mersea Homes (Westerfield) Limited | Construction | 2010 |
| Mersea Homes Group Limited | Construction | 2020 |
| Mersea Island Brewery & Vineyard Ltd | Manufacturing | 2018 |
| Mersea Island Community Trading Company Limited | Hospitality | 1987 |
| Mersea Island Fish Bar Ltd | Real estate | 2010 |
| Mersea Island Fish Ltd | Wholesale & retail | 2024 |
| Mersea Island Storage Ltd | Transport & logistics | 2020 |
| Mersea Island Watersports Limited | Arts & recreation | 2015 |
| Mersea KEN SA Jujitsu Ltd | Arts & recreation | 2025 |
| Mersea Lake and Leisure Limited | Administrative & support | 2024 |
| Mersea Life Ltd | Extraterritorial | 2013 |
| Mersea Media Limited | Information & communication | 2016 |
| Mersea Millsy Limited | Professional & scientific | 2024 |
| Mersea Mudcakes Ltd | Manufacturing | 2018 |
| Mersea Mudd Shack Ltd | Manufacturing | 2020 |
| Mersea Mutts Ltd | Other services | 2021 |
| Mersea Property Management Limited | Real estate | 2006 |
| Mersea Solutions Ltd | Professional & scientific | 2025 |
| Mersea Trading Ltd | Construction | 2023 |
| Mersea Trailers Limited | Manufacturing | 1996 |
| Mersea Trawlers Limited | Agriculture & fishing | 2011 |
| Mersea Water Park Ltd | Hospitality | 2024 |
| Mersh Holdings Limited | Professional & scientific | 2017 |
| Merton Worcester Limited | Real estate | 2016 |
| Meru Consulting Limited | Information & communication | 2020 |
| Mesa Telecom Consultancy Ltd | Information & communication | 2020 |
| Meslektashlar Ltd | Wholesale & retail | 2025 |
| Messina Capital Limited | Administrative & support | 2025 |
| Messina Hembry Clothing Ltd | Wholesale & retail | 2014 |
| Messina Hembry Holdings Ltd | Real estate | 2019 |
| Metacomputics Labs Ltd | Information & communication | 2021 |
| Metal Armour Roofing Ltd | Construction | 2021 |
| Metallic Elephant Limited | Manufacturing | 2019 |
| Metallon Limited | Manufacturing | 1985 |
| Meter Macs Limited | Information & communication | 2011 |
| Metrarc Limited | Information & communication | 2009 |
| Metropolitan Mortgage Solutions Ltd | Professional & scientific | 2014 |
| Mevorach Ltd | Health & social care | 2020 |
| Mewj Pro Ltd | Health & social care | 2019 |
| Meyrick Building Solutions Limited | Construction | 2005 |
| MF Essex Limited | Hospitality | 2017 |
| MF Professional Services Ltd | Construction | 2022 |
| MF Sporting Services Limited | Professional & scientific | 2025 |
| MG Laurel Homes Ltd | Real estate | 2025 |
| MG New Horizons Consulting Ltd | Administrative & support | 2021 |
| MGA Capital Limited | Financial services | 2008 |
| MGA Homes Ltd | Real estate | 2023 |
| MGE Group Ltd | Information & communication | 2026 |
| MGK Digital Solutions Limited | Manufacturing | 2011 |
| MGK Healthcare Limited | Health & social care | 2018 |
| MGK Investments Limited | Construction | 2001 |