| Name/Location | County | Open | Close | Comment |
| Ma Pardoe's | . | . | . | See Old Swan |
| MACLACHLAN'S BAR, Glasgow | Strathclyde | 1999 | 2001 | . |
| MACLAY, Alloa | Central | 1830 | 1999 | Thistle brewery. See also Belhaven |
| McBRIDE'S, Newton Abbot | Devon | 2003 | . | Located at The Dartmouth Inn |
| McCOWANS, Edinburgh | Lothian | 1999 | 2003 | Scottish Courage brewpub |
| McDONNELLS, Charlton | London SE7 | 1983 | 1990 | Plant ex Chudley. Moved from Queen Victoria, Woolwich 1986/7 |
| McGuinness | . | . | . | See Thomas McGuinness |
| McMULLEN, Hertford | Hertfordshire | 1827 | . | Also brews for Hanseatic. IFBB Member |
| MAGUIRE'S, Dublin | Ireland | 1999 | . | Aka Messrs Maguires. Beers served under gas pressure |
| MAIDEN OAK, Ballymagroarth, Londonderry | N I | 1985 | 1989 | Keg only. Aka Foil/Foyle? |
| Malcolms Ales | . | . | . | See Strathore |
| MALDON BREWING, Maldon | Essex | 2003 | . | Stables Brewery. Located at The Blue Boar Hotel |
| MALLARD, Carlton | Nottinghamshire | 1995 | . | . |
| MALTON, Malton | N Yorkshire | 1984 | 2004 | Located at The Crown Hotel. Aka Suddaby's. Plant sold to Thornbridge Hall |
| MALVERN CHASE, Leigh Sinton | Worcestershire | 1980 | 1984 | Aka Coach House |
| MALVERN HILLS, North Malvern | Worcestershire | 1998 | . | . |
| MAN IN THE MOON, Bitteswell, Lutterworth | Leicestershire | 1996 | 1998 | Moved from Ashby Magna 1997. See also Shepherd & Co |
| Mann Crossman & Paulin | . | . | . | See Watney, Whitechapel |
| MANSFIELD, Littleworth, Mansfield | Nottinghamshire | 1855 | 2001 | See also North Country. Acquired by Wolverhampton & Dudley 1999 |
| Mansfield Arms | . | . | . | See Devon Ales |
| MANX ARMS, Barnsley | S Yorkshire | 1992 | 1994 | . |
| MAPLE LEAF, Newark-on-Trent | Nottinghamshire | 1982 | 1986 | Allied (Tetleys) pub brewery |
| Mapledurham Arms | . | . | . | See Butler's |
| MARBLE, Manchester | Gtr Manchester | 1997 | . | Brewery at The Marble Arch PH. Beers are organic |
| Marble Arch | . | . | . | See Marble |
| MARCHES, Claston Dormington | Herefordshire | 1995 | . | Used ex Solstice plant at Leominster until 2001. Restarted 2004 |
| Mardle Hall | . | . | . | See Buffy's |
| Marisco Tavern | . | . | . | See Lundy Island |
| MARKET, Borough Market | London SE1 | 1985 | 1988 | Located at The Market Porter PH. Aka Beache's Ales. Also brewed 81-84 |
| Market Porter | . | . | . | See Market |
| Marlow Brewery | . | . | . | See Wethereds |
| MARSTON MOOR, Kirk Hammerton | N Yorkshire | 1983 | . | Moved from Long Marston 1988 |
| Marston, Thompson & Evershed | . | . | . | See Marston's |
| MARSTON'S, Burton-upon-Trent | Staffordshire | 1834 | . | Aka Marston, Thompson & Evershed. See also Border. Owned by Wolverhampton & Dudley |
| MARTIN, Lincoln | Lincolnshire | 1988 | 1991 | . |
| MARTIN ALES, Dover | Kent | 1983 | 1988 | Continued intermittently until 1990 |
| Martin Elms Wines | . | . | . | See Nethergate |
| MARTLET, Eastbourne | E Sussex | 1979 | 1983 | . |
| MASH, Great Portland St | London W1 | 1998? | . | Beers served under gas pressure |
| MASH & AIR, Manchester | Gtr Manchester | 1996 | 2000? | Restuarant Brewery! |
| Mash Tun | . | . | . | See Lawn |
| Masons Arms, Lower Odcombe | . | . | . | See Odcombe |
| MASONS ARMS, South Leigh | Oxfordshire | 1974 | 1982 | . |
| Masons Arms, Strawberry Bank | . | . | . | See Lakeland & Strawberry Bank |
| MASSEY, Burnley | Lancashire | 1750 | 1974 | Acquired by Bass 1966 |
| MATTHEW BROWN, Blackburn | Lancashire | 1830 | 1991 | Lion Brewery. See also Carlisle, Cleator Moor, T&R Theakston & Workington. Acquired by S&N 1987 |
| MAULDONS, Sudbury | Suffolk | 1982 | . | . |
| MAYFLOWER, Standish, Wigan | Gtr Manchester | 2001 | . | Ceased 2003. Moved to behind the The Royal Oak PH 2004 |
| Mayhems | . | . | . | See Farmers Arms |
| MAYPOLE, Eakring, Newark | Nottinghamshire | 1995 | . | Plant ex Springhead. Same ownership as Milestone |
| MEANTIME, Greenwich | London SE7 | 2000 | . | Specialist/classic-style brewer. Also brews for Freedom |
| MEESONS, Oxford | Oxfordshire | Unconfirmed | . | Source: New Imbiber No.4 |
| MELBOURN, Stamford | Lincolnshire | 1825 | 1974 | See also Melbourn Brothers |
| MELBOURN BROTHERS, Stamford | Lincolnshire | 1999 | . | All Saints Brewery using ex Melbourn plant. Belgian style fruit bottled beers only. Owned by Samuel Smith |
| Melvich Hotel | . | . | . | See Far North |
| MENDIP, Temple Cloud | Somerset | 1978 | 1984 | Mendip United 82-84 |
| Merivales Ales | . | . | . | See Warden |
| MERLIN'S, Ystradgynlais, Swansea | Mid Wales | 1999 | 1999 | Ex Brecknock |
| MERRIMANS, Leeds | W Yorkshire | 1994 | 1998? | Aka Old Fart |
| Mersey Brewery | . | . | . | See Higsons |
| Messrs Maguires | . | . | . | See Maguires |
| Mexborough | . | . | . | See Concertina |
| MICKLES, Walkern | Hertfordshire | 1982 | 1984 | Moved from Lilley 1983 |
| MIDDLETON'S, St Helen Auckland | Co Durham | 1996 | 1998 | Located at The Wheatsheaf PH. Moved from Barnard Castle 1997 |
| MIGHTY OAK, Maldon | Essex | 1996 | . | Plant ex Whitworth Hall. Moved from Brentwood 2000 |
| Mildly Mad Pub Co | . | . | . | See Tynemill & York |
| MILDMAY, Holbeton | Devon | 1993 | 1997 | . |
| MILESTONE, Cromwell, Newark | Nottinghamshire | 2004 | . | Plant ex Dwan. In same ownership as Maypole |
| MILK STREET, Frome | Somerset | 1999 | . | Located at The Griffin PH |
| Mill Ale | . | . | . | See Whitewater |
| MILL, Newton Abbot | Devon | 1983 | 1997 | . |
| MILLENNIUM, Old Knebworth | Hertfordshire | No brewery | . | Beers brewed by Bass Museum for the Lytton Arms |
| MILLER'S THUMB, Anniesland, Glasgow | Strathclyde | 1998 | 2001? | Canal American style restaurant brewery. Owned by Big Beat Group. Beers filtered & carbonated |
| MILLGATE, Failsworth | Gtr Manchester | 1994 | 1996 | Plant sold to Bridgewater Ales |
| MILLIS, South Darenth, Dartford | Kent | 2002 | . | Moved from Gravesend 2003 |
| MILLSTONE, Mossley, Ashton-under-Lyne | Gtr Manchester | 2003 | . | . |
| MILLWRIGHT'S ARMS, Coten End | Warwickshire | 1998 | 1998 | Pub brewery. Closed by Punch Taverns |
| MILTON, Milton, Cambridge | Cambridgeshire | 1999 | . | . |
| Min Pin Inn | . | . | . | See North Cornwall |
| MINERS ARMS, Westbury Sub Mendip | Somerset | 1973 | 1990 | Moved from Priddy 1981 |
| Minera | . | . | . | See City Arms |
| MINERVA, Hull | E Yorkshire | 1994 | 1999 | Carlsberg Tetley pub brewery. Also brewed 85-89 |
| Ministry of Ale | . | . | . | See Moonstone |
| MINNIS, Stelling Minnis, Canterbury | Kent | 1995 | 1996 | Located at The Rose & Crown PH. Closed by Pubmaster |
| MISKIN ARMS, Pontyclun | Glamorgan | 1976 | 1979 | . |
| Mitchells & Butler | . | . | . | See Coors Smethwick |
| MITCHELLS, Lancaster | Lancashire | 1880 | 1999 | Bought ex Yates & Jackson brewery 1985 |
| MIX, Watford | Hertfordshire | 1996 | 1998 | Also a DIY Brewery |
| MOLE'S, Melksham | Wiltshire | 1982 | . | Located on Cascade Drinks site |
| MONMOUTH FINE ALES, Monmouth | Gwent | 1983 | 1986 | Located at The Queens Head PH |
| MONO, Glasgow | Strathclyde | 2003 | . | Restaurant brewery |
| MOONSTONE, Burnley | Lancashire | 2000 | . | Located at the Ministry of Ale (formerly Lord Nelson) PH |
| MOOR BEER Co, Ashcott, Bridgwater | Somerset | 1996 | . | Site shared with Juwards? |
| MOORHOUSE'S, Burnley | Lancashire | 1865 | . | Recommenced real ale brewing 1978 |
| MORDUE, Shiremoor, North Shields | Tyne & Wear | 1995 | . | . |
| Morgans | . | . | . | See Norwich |
| MORLAND, Abingdon | Oxfordshire | 1711 | 2000 | Acquired by Greene King 1999 (plus Ruddles brands) |
| MORRELL, Oxford | Oxfordshire | 1782 | 1998 | Pubs sold to Morrells of Oxford |
| MORRELLS of OXFORD, Oxford | Oxfordshire | No brewery | . | Purchased Morrell estate & brands 1998. See also Thomas Hardy. Most pubs acquired by Greene King 2002 |
| MOULIN, Pitlochry, Perthshire | Tayside | 1995 | . | Located at The Moulin Hotel. Owned by RTR Catering |
| Mount Murray | . | . | . | See Bushys |
| MR CHERRYS, St Leonards | E Sussex | 1984 | 1985 | . |
| Mrs Lewis's | . | . | . | See All Nations |
| MUNDANE ALES, Burton-upon-Trent | Staffordshire | 1993 | 1994 | Plant ex Keystone |
| MUNSLOW, Munslow | Shropshire | 1994 | 2001? | Located at The Munslow (formerly Crown) Inn. Beers now contract brewed by ? |
| Murphy | . | . | . | See Evesham |
| MURPHYS, Cork | Ireland | 1856 | . | Keg only |
| Museum | . | . | . | See Coors, Burton-upon-Trent |