| Manor Road Nursery Limited | Hampshire | 1984 |
| Manor Wood Limited | Beverley | 2008 |
| Manorcove Limited | Gardenstown | 2005 |
| Manorfields Farm Limited | Shrewsbury | 2018 |
| Manorwall Estates Ltd | Holywell | 2004 |
| Manosa Ltd | Manchester | 2021 |
| Mansell Park Farm Limited | Uttoxeter | 2015 |
| Mansfield Canine Centre Ltd | Mansfield | 2019 |
| Mansfield Greosn Limited | Canterbury | 2017 |
| Manson Green Farm Limited | Hingham | 2020 |
| Mantel Equestrian Ltd | Tadley | 2024 |
| Mantel Farm Limited | Catsfield | 2008 |
| Manterra Limited | York | 2011 |
| Mantis (Eco) Ltd | Derby | 2021 |
| Manton Common Renewables Limited | Brigg | 2026 |
| Manton Park Racing Limited | Marlborough | 1973 |
| Manutex Ltd | Alcester | 2025 |
| Man’S Best Friend Kensington and Chelsea Ltd | London | 2020 |
| MAP Haulage Watford Ltd | Watford | 2024 |
| MAP of AG Solutions Limited | Penrith | 2006 |
| Maple Consultancy Limited | Shrewsbury | 2008 |
| Maple Farm Firewood Limited | Petersfield | 2024 |
| Maple Farms (Billinghay) Limited | Lincoln | 2010 |
| Maple Hayes Home Farm Limited | Rugeley | 1950 |
| Maple Manor Woodland Ltd | London | 2023 |
| Maple Tree and Forestry Services Limited | Houghton Le Spring | 2026 |
| Maple Tree Dog Training Ltd | Newent | 2025 |
| Maple Tree Surgery Limited | Leigh-On-Sea | 2007 |
| Maple Valley Equestrian Centre Ltd | Chesham | 2024 |
| Maplebeck Farming Ltd | Newark | 2001 |
| Maplepark Farms UK Ltd | Horsham | 2025 |
| Maplestead Farm Limited | Halstead | 2019 |
| Maplethorpe Contractors Limited | Lincoln | 2009 |
| Mapleton Growers Ltd | Brentwood | 2000 |
| Maplewood Tree Surgery Limited | Brighton | 2023 |
| Mapp Developments Limited | Dronfield | 1997 |
| Mappleborough Green Farm Ltd | Birmingham | 2012 |
| Mapstone Farms Limited | Glastonbury | 2017 |
| MAQ Laboratories Limited | London | 2023 |
| Mara Marine Services Limited | Castlebay | 2025 |
| Mara Mhor Limited | Bunessan | 2025 |
| Mara NA Mara Limited | Forres | 2013 |
| Maragota Properties Limited | Colchester | 2004 |
| Maratech Services Ltd | Fraserburgh | 2025 |
| Marbert Limited | Castle Douglas | 2015 |
| Marble Vineyard Ltd | Canterbury | 2023 |
| Marblelane Limited | Ely | 2000 |
| Marc Hill Farriery Ltd | Carnoustie | 2009 |
| Marcan Limited | Ballykelly | 2011 |
| Marcel's Gardening Ltd | Stoke-On-Trent | 2022 |
| Marcgoodfellow UK Commercial Holding Ltd | Cardiff | 2021 |
| March CFC Limited | March | 2001 |
| March Farmers (Washland) Limited | Sandy | 1972 |
| March Farriers Limited | Exeter | 2013 |
| March Hare Floral Design Limited | Bury St. Edmunds | 2016 |
| March Hare Stud Ltd | Godalming | 2023 |
| March Oaks Ltd | Stocksfield | 2025 |
| March Stud Limited | Maidwell | 2019 |
| March Yard Ltd | Northampton | 2012 |
| Marcham Farms Limited | Salisbury | 1996 |
| Marchburn Farms Limited | Banchory | 1997 |
| Marcher Apple Network | Shrewsbury | 1999 |
| Marches Forestry Services Ltd | Aberystwyth | 2021 |
| Marchetti Holdings Limited | Newbury | 1986 |
| Marchfont Limited | Stratford-Upon-Avon | 2017 |
| Marchingtonbank Services Limited | London | 2025 |
| Marchmont Farms Limited | Wimborne | 1983 |
| Marcombe Valley Farms Limited | Somerset | 1979 |
| Marcon Gamestock Limited | York | 1981 |
| Marcs Seafood Limited | Torpoint | 2025 |
| Marcstown Ltd | Newmarket | 2024 |
| Marcus H Oliver Pigs Limited | Fakenham | 2011 |
| Marcus Rickard Agricultural Services Ltd | Newport | 2015 |
| Marcus Wells Fencing Limited | Haslemere | 2014 |
| Marda Associates Limited | Ledbury | 1998 |
| Mardan Poultry Limited | Enniskillen | 2015 |
| Mardon Havstor Ltd | Lancaster | 1983 |
| Mardon Limited | Lancaster | 1984 |
| Mareel Fishing Company Ltd | Yell | 2011 |
| Marelands Farms Ltd | Farnham | 2019 |
| Marelann Fishing Ltd | Western Isles | 2013 |
| Mareneve Ltd | London | 2026 |
| Margaretting Hall Farms Ltd | Stock | 2021 |
| Margent Farm Limited | Cambridge | 2017 |
| Marginal Grains Ltd | London | 2025 |
| Margmore Enterprises Ltd | Aberfeldy | 2024 |
| Margot's Farm Ltd | Taunton | 2025 |
| Margrie Limited | Edinburgh | 1992 |
| Marham Hall Farms Limited | Kings Lynn | 1959 |
| Marial Gwyn Limited | Northwich | 2022 |
| Marianne North Centre Hastings Ltd | Hastings | 2024 |
| Marie Bauer Ltd | Burton-On-Trent | 2023 |
| Marigold A52 Limited | Edinburgh | 2025 |
| Marigold Farming Company Limited | Berwickshire | 1962 |
| Marine and Steam Ltd | Liskeard | 2007 |
| Marine Aquatics Limited | Walsall | 2013 |
| Marine Biotech Limited | Aultbea | 2022 |
| Marine Discovery Centre Whitby CIC | Whitby | 2022 |
| Marine Ecosystems Regeneration Ltd | Winchester | 2024 |
| Marine Farm Aquatics Ltd | Oakham | 2018 |