- Lagan Valley 1983-
- Lambeth 1832-1885
- Lambeth Brixton 1885-1974
- Lambeth Central 1974-1983
- Lambeth Kennington 1885-1950
- Lambeth North 1885-1950
- Lambeth Norwood 1885-1983
- Lambeth Streatham 1974-1983
- Lambeth Vauxhall 1950-1983
- Lanark 1708-1832
- Lanark 1918-1983
- Lanark and Hamilton East 2005-
- Lanarkshire 1708-1868
- Lanarkshire Mid 1885-1918
- Lanarkshire North 1950-1983
- Lanarkshire North Eastern 1885-1918
- Lanarkshire North Western 1885-1918
- Lanarkshire Northern 1918-1950
- Lanarkshire Northern 1868-1885
- Lanarkshire Southern 1868-1918
- Lancashire 1660-1832
- Lancashire North Eastern 1868-1885
- Lancashire Northern 1832-1885
- Lancashire South Eastern 1868-1885
- Lancashire South Western 1868-1885
- Lancashire Southern 1832-1868
- Lancashire West 1983-
- Lancaster 1660-1866
- Lancaster 1885-1997
- Lancaster and Wyre 1997-
- Langbaurgh 1983-1997
- Launceston 1660-1918
- Leeds 1832-1885
- Leeds Central 1885-1955
- Leeds Central 1983-
- Leeds East 1885-1918
- Leeds East 1955-
- Leeds North 1885-1955
- Leeds North East 1918-
- Leeds North West 1950-
- Leeds South 1885-1983
- Leeds South East 1918-1983
- Leeds South and Morley 1983-1997
- Leeds West 1885-
- Leek 1885-1983
- Leicester 1660-1918
- Leicester East 1918-1950
- Leicester East 1974-
- Leicester North East 1950-1974
- Leicester North West 1950-1974
- Leicester South 1974-
- Leicester South 1918-1950
- Leicester South East 1950-1974
- Leicester South West 1950-1974
- Leicester West 1918-1950
- Leicester West 1974-
- Leicestershire 1660-1832
- Leicestershire North West 1983-
- Leicestershire Northern 1832-1885
- Leicestershire Southern 1832-1885
- Leigh 1885-
- Leith 1918-1950
- Leith District of Burghs 1832-1918
- Leitrim 1802-1885
- Leitrim 1918-1922
- Leitrim North 1885-1918
- Leitrim South 1885-1918
- Leominster 1660-
- Lewes 1660-
- Lewisham 1885-1918
- Lewisham Deptford 1974-
- Lewisham East 1974-
- Lewisham East 1918-1950
- Lewisham North 1950-1974
- Lewisham South 1950-1974
- Lewisham West 1918-
- Leyton 1950-1997
- Leyton East 1918-1950
- Leyton West 1918-1950
- Leyton and Wanstead 1997-
- Lichfield 1660-1950
- Lichfield 1997-
- Lichfield and Tamworth 1950-1983
- Limerick 1802-1922
- Limerick 1802-1885
- Limerick East 1885-1922
- Limerick West 1885-1922
- Lincoln 1660-
- Lincolnshire 1660-1832
- Lincolnshire Mid 1868-1885
- Lincolnshire Northern 1868-1885
- Lincolnshire Southern 1868-1885
- Lincolnshire, parts of Kesteven and Holland 1832-1868
- Lincolnshire, parts of Lindsey 1832-1868
- Linlithgow 1983-2005
- Linlithgow and East Falkirk 2005-
- Linlithgowshire 1708-1950
- Linsey East 1983-1997
- Lisburn 1802-1885
- Liskeard 1660-1885
- Littleborough and Saddleworth 1983-1997
- Liverpool 1660-1885
- Liverpool Abercromby 1885-1918
- Liverpool Broadgreen 1983-1997
- Liverpool East Toxteth 1885-1950
- Liverpool Edge Hill 1918-1983
- Liverpool Everton 1885-1950
- Liverpool Exchange 1885-1974
- Liverpool Fairfield 1918-1950
- Liverpool Garston 1950-
- Liverpool Kirkdale 1885-1983
- Liverpool Mossley Hill 1983-1997
- Liverpool Riverside 1983-
- Liverpool Scotland 1885-1974
- Liverpool Scotland Exchange 1974-1983
- Liverpool Toxteth 1950-1983
- Liverpool Walton 1885-
- Liverpool Wavertree 1997-
- Liverpool Wavertree 1918-1983
- Liverpool West Derby 1885-
- Liverpool West Toxteth 1885-1950
- Livingston 1983-
- Llandaff and Barry 1918-1950
- Llanelli 1950-
- Llanelly 1918-1950
- London University 1832-1950
- Londonderry 1801-1885
- Londonderry 1922-1983
- Londonderry 1802-1922
- Londonderry East 1983-
- Londonderry North 1885-1922
- Londonderry South 1885-1922
- Longford 1802-1885
- Longford 1918-1922
- Longford North 1885-1918
- Longford South 1885-1918
- Lonsdale 1918-1950
- Lostwithiel 1661-1832
- Loughborough 1885-
- Louth 1885-1983
- Louth 1832-1885
- Louth 1918-1922
- Louth North 1885-1918
- Louth South 1885-1918
- Louth and Horncastle 1997-
- Lowestoft 1885-1983
- Ludgershall 1660-1832
- Ludlow 1660-
- Luton 1885-1974
- Luton East 1974-1983
- Luton North 1983-
- Luton South 1983-
- Luton West 1974-1983
- Lyme Regis 1660-1868
- Lymington 1660-1885
2,145 constituencies in total