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Warning: This is not intended to be an exhaustive history of the companies listed, but an indication of the changes of ownership and the links between companies and directors in those companies. Only collieries, pits etc. in the North of England are shown - the companies may own other properties etc. outside this area and there may have been other changes of ownership etc. for which we currently do not have details.
Entries added or updated since 01 Jun 2008 are highlighted thus: 
| Company | Company Details | |
|---|---|---|
| Ladythorne Coal Co. Ltd. | ||
| Lambley Coal Co. Ltd. | 1924, 1933, 1940, 1947 | |
|
Lambton & Hetton Collieries Ltd. | 1923 |
| Lambton Collieries Ltd. | ||
|
Lambton, Hetton & Joicey Collieries Ltd. | 1933, 1940, 1947 |
| Lanchester & Iveston Coal Co. Ltd. | 1933, 1940, 1947 | |
| Langley Barony Fireclay Co. Ltd. | 1933, 1940 | |
| Langley Barony, Coal & Fireclay Co. Ltd. | 1923 | |
| Langley Brick Co. Ltd. | ||
| Langleydale Coal Co. Ltd. | ||
| Langness Copper Co. Ltd. | ||
| Laporte Chemicals Ltd. | ||
| Laycock, Joseph & Co. | ||
| Leadgate Coal Co. Ltd. | ||
| Leconfield, Lord | 1888, 1921, 1930 | |
| Lemington Colliery Co. Ltd. | 1933 | |
| Leverson's Wallsend Collieries Ltd. | 1923, 1933, 1940 | |
| Lindow, S. & J. | ||
| Livingston Refractories Ltd. | 1940, 1947 | |
| London Lead Co. | ||
|
Londonderry Collieries Ltd. | 1923, 1933, 1940, 1947 |
| Long Fell Barytes Ltd. | ||
| Long Framlington Coal Co. Ltd. | ||
| Long Meg Plaster & Mineral Co. Ltd. | ||
| Lonsdale Mining Co. Ltd. | ||
| Lord Leconfield | 1888, 1921, 1930 | |
| Low Beechburn Coal Co. Ltd. | 1923 | |
| Lower Butterknowle Colliery (1957) Ltd. | ||
| Lowson, Henry Ltd. | 1923, 1933 |
