| Marine Farm Services Limited | Waterlooville | 2020 |
| Marine Fishing Limited | Romford | 2025 |
| Marine Hatchery Consultancy Ltd. | Mansfield | 2017 |
| Marine Larder Limited | Eyemouth | 2020 |
| Marine Mesh Services Limited | Chichester | 2015 |
| Marine Stewardship Council | London | 1997 |
| Marine Stewardship Council International Limited | London | 1997 |
| Marine Trader Ltd | Copthorne | 2018 |
| Marine-Fish World Limited | Stony Stratford | 2017 |
| MARINE23 Limited | Nether Alderley | 2014 |
| Marineco Limited | Saltash | 2012 |
| Marinet Limited | Bromsgrove | 2014 |
| Marini Bloodstock Limited | Jedburgh | 2025 |
| Marisa KOI Farm Limited | Milton Keynes | 2016 |
| Maritime Crewing Solutions Ltd | Isle Of Barra | 2024 |
| Marivate Limited | St. Andrews | 2022 |
| Marjwood Ltd | Middleton | 2009 |
| Mark Allsop Thatching Limited | Swindon | 2014 |
| Mark Andrew Limited | Truro | 2010 |
| Mark Barrett Livestock Transport Ltd | Radstock | 2021 |
| Mark Barton Farriers Limited | Titchfield | 2009 |
| Mark Black Farming Ltd | Southampton | 2011 |
| Mark Brunsdon Property Limited | Yelverton | 2019 |
| Mark Caudwell Limited | Berwick-Upon-Tweed | 1988 |
| Mark Connelly Conservation Ltd | Chester Le Street | 2012 |
| Mark Davey Limited | Petersfield | 1997 |
| Mark Digby (Netherlands) Limited | Loughborough | 2007 |
| Mark Fiddes Tree Works Ltd | Weston-Super-Mare | 2008 |
| Mark Fletcher Productions Limited | Swindon | 1993 |
| Mark Fullerton Marine Services Limited | Bridge End | 2024 |
| Mark Goatley Limited | Northampton | 2003 |
| Mark Gurowich Ltd | Evershot | 2012 |
| Mark H Poskitt Limited | Goole | 1956 |
| Mark Hill Farms Limited | Edinburgh | 1976 |
| Mark Hinsley Arboricultural Consultants Limited | Wimborne | 2010 |
| Mark Ireland Contracting Services Ltd | Workington | 2012 |
| Mark JD Adamson Limited | Ashford | 2009 |
| Mark Johnson Limited | | 2005 |
| Mark Kemp Farms Ltd | Stockbridge | 2011 |
| Mark Lawton Limited | Barnsley | 2006 |
| Mark Little (Farms) Limited | Manchester | 1982 |
| Mark Lloyd Trees Ltd | Carlisle | 2025 |
| Mark Newell Tree Care Ltd | Bidford-On-Avon | 2014 |
| Mark Oglesby Sprayer Services Ltd | York | 2011 |
| Mark Osborne Farriers Limited | Bonnybridge | 2010 |
| Mark Paterson Farms Limited | Radstock | 2025 |
| Mark Peachey Contracting Limited | Burwell | 2012 |
| Mark Pearson HGV Driving Services Limited | Bury | 2017 |
| Mark Randall Associates Limited | Guildford | 2004 |
| Mark Riding Ltd | Blackburn | 2019 |
| Mark Robertson (Scotland) Ltd. | Banff | 2016 |
| Mark S Thompson Timber Contractors Limited | Bakewell | 2004 |
| Mark Seed Forest and Land Management Limited | Langholm | 2012 |
| Mark Shotton Limited | Co Durham | 2006 |
| Mark Skipworth & SON Farming Ltd | Boston | 2022 |
| Mark Skipworth & SON Ltd | Boston | 2025 |
| Mark Stalham Potato Consultancy Ltd | Cambridge | 2020 |
| Mark Titley Limited | Crewe | 2019 |
| Mark Warkup Limited | Driffield | 2012 |
| Mark Weatherhead Limited | Royston | 1981 |
| Mark Whatley Tree Services Ltd | Chesterfield | 2003 |
| Mark Wilkinson Investments Limited | Wellingborough | 2003 |
| Mark Worboys Tree Surgery Limited | Poole | 2015 |
| Mark.S.Hoseason Ltd | Shetland | 2013 |
| Markate Gardens C.I.C. | Northchurch | 2024 |
| Markcourt Limited | Devon | 1999 |
| Market Harborough Honey Co. Limited | Coventry | 2019 |
| Markfield Farm Ltd | Lytham St. Annes | 2026 |
| Markham Grange Garden Centre Ltd | Chorley | 2021 |
| Markitt Limited | Norwich | 2013 |
| Markmoor Limited | Bristol | 1979 |
| Marko and SON Ltd | Downham Market | 2025 |
| Markrite Limited | Industrial Estate, Launceston | 2005 |
| Marks Barn Farm (Crewkerne) Limited | Crewkerne | 1960 |
| Marks Hall Farms Limited | Great Dunmow | 1959 |
| Marks Hall Shooting Syndicate Limited | Colchester | 2006 |
| Marks Walks Dog Services Ltd | Glasgow | 2025 |
| Marland Marine Services Limited | Flint Mountain | 2009 |
| Marlbrook Bloodstock Limited | Redditch | 2020 |
| Marlex Limited | Aberdeenshire | 2003 |
| Marley & ME Dog Walking Company Ltd | Leeds | 2021 |
| Marley Combe Technical Services Ltd | Holsworthy | 2017 |
| Marley Hill Estates Ltd | Newcastle Upon Tyne | 2016 |
| Marleys Farm Ltd | Bedale | 2015 |
| Marlin Agri Ltd | Alford | 2024 |
| Marlingford Trading Limited | Norwich | 2025 |
| Marlow Management Limited | London | 1996 |
| Marlsbrough Farm Limited | Haverfordwest | 2003 |
| Marmag Fishing Services Ltd | Lossiemouth | 2019 |
| Marnoch Contractors Limited | | 2000 |
| Marnwood Acquisitions Ltd | Telford | 2023 |
| Maro Consultancy Ltd | Wisbech | 2022 |
| Maroon (Eco) Ltd | Derby | 2021 |
| Marouk Consulting Ltd | Woking | 2017 |
| Marple Farming Limited | Chorley | 2016 |
| Marquand Agri Limited | Bodmin | 2022 |
| Marr Grange Farm Limited | Doncaster | 2012 |
| Marr Management Limited | Park Ferriby Road Hessle | 2005 |
| Marrick Lodge Farm Ltd | Richmond | 2025 |
| Marriott Fishing Company Limited | Southwold | 2024 |