| Alba Gaskets Limited | Aberdeen | 2007 |
| Albion Drilling Services Ltd | Yarmouth | 2022 |
| Albion OIL Ltd | London | 2016 |
| Albion Stone PLC | Nutfield | 1983 |
| Albit Blockchain Ltd | Edinburgh | 2022 |
| ALC Drill Limited | Maidstone | 2021 |
| Alchemygreen UK Limited | London | 2010 |
| Aldridge Stainless & Alloys Ltd | Sutton Coldfield | 2013 |
| Aleena Petroleum UK Limited | Ruislip, | 2023 |
| Alesowest Limited | Whitby | 2013 |
| Alex Adamson & SON Limited | Aberdeen | 2011 |
| Alexander Engineering Services Ltd. | Aberdeenshire | 2007 |
| Alexander OIL and GAS Solutions Ltd | Glasgow | 2025 |
| Alexander Ross & Sons (Sand and Gravel) Limited | Aberdeen | 1964 |
| Alexiam Materials Consulting Limited | Rochford | 2015 |
| Alfa Corp OG Ltd | London | 2026 |
| Alfa Star Global (UK) Ltd. | London | 2022 |
| Alfanoil UK Ltd | London | 2025 |
| Alff Integrated Services Ltd | London | 2017 |
| Alfred H Knight Mineral Processing UK Limited | Truro | 2002 |
| Alfred Mcalpine Slate Limited | Wolverhampton | 1971 |
| ALG Engineering Services Ltd | Saltburn-By-The-Sea | 2021 |
| Algoldenone Limited | London | 2021 |
| ALH Engineering Services Ltd | Bucksburn | 2020 |
| ALI Bros Enterprises Ltd | Manchester | 2013 |
| ALI Global International Trading (UK) Company Limited | Cardiff | 2025 |
| Alien Space Works Limited | Cardiff | 2021 |
| Alion Engineering Solutions Ltd | Aberdeen | 2015 |
| Aliveups Limited | Balmedie | 2010 |
| Aliwal Industries Ltd | Royston | 2022 |
| ALJ NE Solutions Ltd | Wallsend | 2022 |
| ALL Hail Nana Ltd | London | 2019 |
| ALL Terrain Inspections Limited | Doncaster | 2011 |
| Allan Fraser Engineering Ltd | Aberdeen | 2023 |
| Allan Smith Electrical Services Ltd | Dundee | 2019 |
| Allen Newport Limited | Colchester | 1934 |
| Allied Gold Resources Ltd | Surbiton | 2006 |
| Allied OIL & GAS Ltd | Surbiton | 2006 |
| Allison Plant Hire Limited | Sheringham | 2012 |
| Allmech Limited | Lowestoft | 2015 |
| Allmech Services Ltd | Lowestoft | 2016 |
| Allstar Access Ltd | Edinburgh | 2020 |
| Allstone Holdings Limited | Gloucester | 2021 |
| Allstone Sands Gravels Aggregates Trading Co. Ltd. | Gloucester | 1983 |
| Almarwa Group Ltd | Redhill | 2025 |
| Alpha Development Solutions Ltd | Harrow | 2026 |
| Alpha Firm Ltd | Montrose | 2019 |
| Alpha OIL Liberia Limited | London | 2020 |
| Alpha Petroleum Services Limited | London | 1994 |
| Alpha Quarry Products Ltd | Belfast | 2010 |
| Alpha Thames Subsea Limited | London | 2005 |
| Alpha Universal Limited | Chertsey | 2018 |
| Alphapit Consulting Limited | Penzance | 2025 |
| Alpine Advanced Access Limited | Falkirk | 2018 |
| Alpine Petroleum Limited | Aberdeen | 2017 |
| ALS Anderson Lifting Services Ltd | Magherafelt | 2025 |
| ALS Holdings Group Limited | Prescot | 2006 |
| ALS Testing Services (UK) Limited | Prescot | 2011 |
| ALS UK (Holdings) Limited | Prescot | 2013 |
| Alsandross Petroleum UK Inc Ltd | London | 2017 |
| Alsi Subsea Operations Ltd | Kirkcaldy | 2019 |
| Alsop Electrical Ltd | Turriff | 2019 |
| Alston Natural Stone Limited | Cumbria | 2002 |
| ALT Resources PLC | London | 2021 |
| Alta Quest Energy Corporation (UK) Limited | Leigh-On-Sea | 1987 |
| Altamaris Frontier Limited | Northampton | 2025 |
| Altera Production UK Limited | Bristol | 1995 |
| Altera Voyageur Production Limited | Westhill | 2007 |
| Alternative Earth Software Limited | Aberdeen | 2024 |
| Alternative SUD Ltd | Enfield | 2025 |
| Alton Road Land Limited | Nuneaton | 2015 |
| Altona Rare Earths Ltd | London | 2026 |
| Altor Consulting Limited | Lichfield | 2020 |
| Altrad Integrity Services Limited | Aberdeen | 1995 |
| Altrad Technical Services (Holdings) Limited | Aberdeen | 2004 |
| Altura Access Ltd. | Edinburgh | 2013 |
| Altus Intervention (ME) Limited | Aberdeen | 2014 |
| Altus Intervention Limited | Aberdeen | 2001 |
| Altus Strategies Limited | London | 2017 |
| Altwood Petroleum Limited | Maidenhead | 1992 |
| Altyngold PLC | London | 2004 |
| ALU Global Supply Limited | Ruislip, | 2026 |
| Alum Garth Minerals Ltd | Whitby | 2012 |
| Alumet Global Ltd | Ruislip, | 2025 |
| Alumina Industries of Guinee Limited | London | 2023 |
| Alung Services Ltd | Edinburgh | 2022 |
| Alveare Ltd | Guildford | 2019 |
| Alyn Evans Consultancy Services Ltd | Glynneath | 2012 |
| AMA OIL and GAS Limited | London | 2024 |
| Amaicba Integrity Services Limited | London | 2023 |
| Amara Mining (Cote D'Ivoire) Limited | Kingston Upon Thames | 2004 |
| Amara Mining Limited | Kingston Upon Thames | 2003 |
| Amarian Holdings Ltd | Hebburn | 2023 |
| Amberforth Limited | | 1994 |
| Ambico Offshore Limited | Brechin | 2011 |
| Ambor Logistics Ltd | Montrose | 2012 |
| Ambrett Holdings Limited | Winchester | 2024 |
| Ambrisbeg Limited | Isle Of Bute | 1992 |
| AMC Property Consultancy Limited | Bourne | 2004 |
| Amco Drilling (UK) Limited | Holmfirth | 2009 |