- Macclesfield 1832-
- Maidenhead 1997-
- Maidstone 1660-1997
- Maidstone and The Weald 1997-
- Makerfield 1983-
- Maldon 1660-1983
- Maldon and Chelmsford East 1997-
- Mallow 1802-1885
- Malmesbury 1660-1885
- Malton 1660-1885
- Manchester 1832-1885
- Manchester Ardwick 1918-1983
- Manchester Blackley 1918-
- Manchester Central 1974-
- Manchester Cheetham 1950-1974
- Manchester Clayton 1918-1955
- Manchester East 1885-1918
- Manchester Exchange 1918-1974
- Manchester Gorton 1918-
- Manchester Hulme 1918-1950
- Manchester Moss Side 1918-1983
- Manchester North 1885-1918
- Manchester North East 1885-1918
- Manchester North West 1885-1918
- Manchester Openshaw 1955-1983
- Manchester Platting 1918-1950
- Manchester Rusholme 1918-1950
- Manchester South 1885-1950
- Manchester South West 1885-1918
- Manchester Withington 1918-
- Manchester Wythenshawe 1950-1997
- Mansfield 1885-
- Marlborough 1660-1885
- Marylebone 1832-1885
- Marylebone East 1885-1918
- Marylebone West 1885-1918
- Mayo 1802-1885
- Mayo East 1885-1922
- Mayo North 1885-1922
- Mayo South 1885-1922
- Mayo West 1885-1922
- Meath 1802-1885
- Meath North 1885-1922
- Meath South 1885-1922
- Medway 1885-
- Meirionnydd Nant Conwy 1983-
- Melton 1885-1983
- Meriden 1950-
- Merioneth 1974-1983
- Merionethshire 1660-1974
- Merthyr Tydfil 1950-1983
- Merthyr Tydfil 1832-1918
- Merthyr Tydfil Aberdare 1918-1950
- Merthyr Tydfil Merthyr 1918-1950
- Merthyr Tydfil and Rhymney 1983-
- Merton Mitcham and Morden 1974-1983
- Merton and Morden 1950-1974
- Mid-Ulster 1950-1974
- Middlesbrough 1832-1918
- Middlesbrough 1983-
- Middlesbrough East 1918-1974
- Middlesbrough South and Cleveland East 1997-
- Middlesbrough West 1918-1974
- Middlesex 1660-1885
- Middleton 1885-1918
- Middleton and Prestwich 1918-1983
- Midhurst 1660-1885
- Midlothian 1955-
- Midlothian and Peeblesshire 1950-1955
- Midlothian and Peeblesshire Northern 1918-1950
- Milborne Port 1660-1832
- Milton Keynes 1983-1992
- Milton Keynes North East 1992-
- Milton Keynes South West 1992-
- Minehead 1660-1832
- Mitcham 1918-1974
- Mitcham and Morden 1983-
- Mitchell 1660-1832
- Mole Valley 1983-
- Monaghan 1801-1885
- Monaghan North 1885-1922
- Monaghan South 1885-1922
- Monklands East 1983-1997
- Monklands West 1983-1997
- Monmouth 1918-
- Monmouth District of Boroughs 1660-1918
- Monmouthshire 1660-1885
- Monmouthshire Northern 1885-1918
- Monmouthshire Southern 1885-1918
- Monmouthshire Western 1885-1918
- Montgomery 1974-1997
- Montgomery District of Boroughs 1660-1918
- Montgomeryshire 1660-1974
- Montgomeryshire 1997-
- Montrose District of Burghs 1832-1950
- Moray 1983-
- Moray and Nairn 1974-1983
- Moray and Nairnshire 1918-1974
- Morecambe and Lonsdale 1950-1983
- Morecambe and Lunesdale 1983-
- Morley 1885-1918
- Morley and Rothwell 1997-
- Morpeth 1660-1983
- Mossley 1918-1950
- Motherwell 1918-1974
- Motherwell North 1983-1997
- Motherwell South 1983-1997
- Motherwell and Wishaw 1974-
2,145 constituencies in total