| London Minerals and Metals Trade Ltd | London | 2022 |
| London Petroleum Solutions Limited | King'S Lynn | 2016 |
| London Reserve Ltd. | Darlington | 2011 |
| London Sahara Gold Ltd | London | 2021 |
| London Tripoli Energy Ltd | London | 2025 |
| Lone Star Drilling Ltd | Stockport | 2022 |
| Long Ashton Design Limited | Cheddar | 2010 |
| Long Offshore Services Ltd | Manchester | 2014 |
| Long Rake Spar Company Limited(The) | Bakewell | 1960 |
| Longch Marine Limited | Dartford | 2015 |
| Longcliffe Quarries Limited | Matlock | 1933 |
| Longfield Energy Consultants Limited | London | 2014 |
| Longland Resources Limited | Bristol | 2016 |
| Longtarget Limited | Banchory | 1988 |
| Longwater (Gravel) Company Limited(The) | Norwich | 1952 |
| Longwood Quarries Limited | Lincoln | 1941 |
| Lonmay Projects Limited | Fraserburgh | 2015 |
| Lonsdale Energy Ltd | Ashington | 2018 |
| Lopez Electrical Ltd | Wallsend | 2011 |
| Loremar Limited | Hornsea | 2005 |
| Lorne Resources Ltd | North Berwick | 2012 |
| LOS Endos Ltd | Nuneaton | 2022 |
| Lothians Rigging & Lifting Ltd | Gorebridge | 2022 |
| Lotus Energy Limited | London | 2018 |
| Loudounhill Contracts Limited | Ayrshire | 1986 |
| Loughdoo Aggregates & Concrete (Ballymena) Ltd | Cookstown | 2011 |
| Loughran Concrete Ltd | Newry | 2014 |
| Loughran Rock Industries (NI) Limited | Mowhen | 2009 |
| Loughran Rock Quarries Ltd | Omagh | 2012 |
| Lovell Stone Group Limited | Cheltenham | 2009 |
| Lovie (New Pitsligo) Limited | Fraserburgh | 1998 |
| Lovie Limited | Fraserburgh | 1994 |
| Lovyino Ltd | London | 2020 |
| LOW Sulphur Fuels Limited | Bournemouth | 2018 |
| Lower Knighton Landfill Limited | Totland Bay | 1993 |
| LP (Origination) Limited | London | 2008 |
| LR 1760 (1) Limited | Kingswells | 2003 |
| LR 1760 (2) Limited | Aberdeen | 2008 |
| LR O&G Limited | Banff | 2016 |
| LR Petroleum and Mining Ltd | London | 2023 |
| LRC Riggers Ltd | London | 2022 |
| LRW Access and Lifting Limited | Hartlepool | 2018 |
| LS Contract Solutions Limited | Dundee | 2018 |
| LS Mining Ltd | Bristol | 2024 |
| LST Coatings Ltd | South Shields | 2014 |
| LSW Services Ltd | Wick | 2021 |
| LTM Rigging Ltd | Sheffield | 2014 |
| Ltro Ltd | | 2002 |
| Lubeck Limited | Nottinghamshire | 1997 |
| Lucas Bolney Limited | London | 2013 |
| Lucas Bowland (NO.2) Limited | London | 2013 |
| Lucas Bowland (UK) Limited | London | 2012 |
| Lucas Holdings (Bolney) Limited | London | 2012 |
| Lucas Holdings (Bowland) Limited | London | 2012 |
| Lucent Resources Limited | Twickenham | 2015 |
| Ludwell Lithium Ltd | Bishop Auckland | 2022 |
| Lukalaba Mining Company Ltd | London | 2024 |
| Luke Maddy and SON Services Ltd | Aberdare | 2023 |
| Lulsgate Quarry Company Limited | Bristol | 1984 |
| Lumalat UK Ltd | London | 2019 |
| Lumonix Trading Ltd | London | 2025 |
| Lunar Mining Company Ltd | Leyburn | 2021 |
| Lundy Services Limited | Fort William | 2019 |
| Lurk Energy Services Ltd | Aberdeen | 2019 |
| Lury Aggregates Limited | Colchester | 2008 |
| Luzern Minerals Limited | Stoke On Trent | 2006 |
| LX Enterprises Ltd | Hexham | 2012 |
| Lycia GEO Consulting Ltd | London | 2021 |
| Lykos Metals (UK) Limited | London | 2022 |
| Lynch Aggregates Limited | Bognor Regis | 2025 |
| Lyndon Pallett (EA) Limited | Hertford | 2012 |
| Lyonesse Consulting Limited | London | 2017 |
| M & J RIG Services Ltd | Whitby | 2017 |
| M & Q Services Ltd. | Callander | 2006 |
| M & Q Special Projects Limited | Rushden | 2017 |
| M and M Yorkshire Stone Products Limited | West Yorkshire | 2004 |
| M C W Limited | Keighley | 2002 |
| M G Well Serv Ltd | Dundee | 2011 |
| M H Piping Engineering Limited | Aberdeen | 2007 |
| M Holliday Engineering Ltd. | Chesterfield | 2016 |
| M I S U Co. Limited | Poole | 2001 |
| M S M Services Ltd | Peterhead | 2012 |
| M S S (Scotland) Limited | Stranraer | 2017 |
| M T W Rigging & Lifting Limited | Middlesbrough | 2016 |
| M V Rope Access Limited | Stockton-On-Tees | 2020 |
| M W Dixon Geoscience Limited | London | 2024 |
| M W Johnston & SON Ltd | Lisburn | 2014 |
| M&J Prynn Ltd | Ivybridge | 2014 |
| M&L Offshore Limited | Seaham | 2014 |
| M&M Graphite UK Ltd | Sutton Coldfield | 2026 |
| M&M Mining International Ltd | Sutton Coldfield | 2025 |
| M&P C. Consulting Ltd | London | 2023 |
| M&R Mining Limited | Craigavon | 2019 |
| M. a. M. Access Limited | Wynyard | 2018 |
| M.A.G.L. Ltd | Southampton | 2026 |
| M.B.Wilkes Limited | Wimborne, Minster | 1964 |
| M.H. Well Works Ltd. | Aberdeen | 2000 |
| M.J. Structural Design Limited | Troon | 2018 |
| M.Mason Well Work Ltd | Dundee | 2026 |
| M.O. RIG Services Limited | Skelmersdale | 2024 |