| Alphagen Capital Limited | Birmingham | 1969 |
| Alphagen Energy Limited | Wrexham | 2025 |
| Alphagen Group Ltd | Chesterfield | 2023 |
| Alphagraph Services Ltd | London | 2025 |
| Alphaliene Limited | London | 2014 |
| Alpham House Management Limited | London | 1986 |
| Alphamed Europe Limited | Craigavon | 2005 |
| Alphant Brand Management Co., Ltd | Coventry | 2024 |
| Alphapet Management Services Limited | Bristol | 2011 |
| Alphasense Trustee Limited | Cambridge | 2014 |
| Alphason Designs Limited | London | 2018 |
| Alphatania Limited | Marlow | 2003 |
| Alphatech Designs Limited | Suffolk | 2000 |
| Alphatheta Limited | Kings Cross, London | 2014 |
| Alphazita Limited | Bingley | 2018 |
| Alpher Ltd | London | 2025 |
| Alpine Answers Limited | Northchapel | 1992 |
| Alpine Exploration Club Limited | City Of Newport | 1992 |
| Alpine Physiotherapy Limited | Harpenden | 2017 |
| Alpine Plumbing Ltd | Ely | 2018 |
| Alpine Property Building Services Limited | London | 2004 |
| Alpine Sports UK Limited | Macclesfield | 2008 |
| Alpine Therapy Ltd | Harpenden | 2016 |
| Alpine UK Construction Ltd | High Wycombe | 2024 |
| Alpinereach Ltd | London | 2020 |
| Alpinerose Limited | Eastbourne | 1982 |
| Alpraham Investments Limited | London | 2013 |
| Alps (UK) Baby Care Products Ltd | London | 2016 |
| Alpy Yachting Ltd | London | 2025 |
| Alqfila Nidal Co., Ltd | London | 2025 |
| Alric Leder Limited | Manchester | 2018 |
| Alrosa Investment Group Co., Ltd | Beckenham | 2021 |
| ALS Flexisure Limited | Hayling Island | 2023 |
| ALS Invest Limited | Maidstone | 2025 |
| Alscot Joinery Limited | Preston On Stour | 2016 |
| Alsham Sweet and Food Factory Limited | Perivale | 2014 |
| Alshamela-Group Co., Ltd | London | 2025 |
| Alsinstallations Limited | Droitwich | 2012 |
| Alsirat TV. Channel Ltd. | London | 2010 |
| Alstom Electronics Limited | Derbyshire | 1994 |
| Alstom Transport Service Ltd | Derby | 1993 |
| Alston Limestone Company (the) Limited | Birmingham | 1908 |
| Alston Trustees Limited | Atherstone On Stour | 2022 |
| Alstron Property Services Ltd. | London | 1999 |
| ALT Customer Solutions Ltd | Renfrew | 2017 |
| ALT I Automatisering Limited | Stockport | 2013 |
| ALT I Juletraer Limited | London | 2010 |
| ALT I Stal Limited | London | 2019 |
| ALT Property Reality Limited | St. Austell | 2024 |
| ALT Spray Cork Ltd | Waltham Abbey | 2023 |
| ALT Trading Ltd | Stockport | 2024 |
| Alta Car and Engineering Company Limited | Evesham | 2016 |
| Alta Performance Materials Limited | London | 2018 |
| Altair 1965 Limited | Salford | 2014 |
| Altaraf Company Ltd | London | 2024 |
| Altaras Marine Limited | London | 2023 |
| Altas Auto UK Limited | Horsham | 2020 |
| Altass-Cheshire Limited | Beverley | 2016 |
| Altcar Limited | London | 2013 |
| Altcom 222 Limited | Altrincham | 1999 |
| Altcom 431 Limited | Warrington | 2007 |
| Altcompany Limited | Carnforth | 2025 |
| Altee Investments Ltd | Hampton | 2019 |
| Alter Knights Group Limited | London | 2023 |
| Alter Vista Ltd. | London | 2017 |
| Altera Aesthetics Ltd | Surrey | 2023 |
| Altermead Limited | Winchester | 1991 |
| Alternativa One Ltd | Harrow | 2023 |
| Alternative Aesthetics Worcester Ltd | Worcester | 2025 |
| Alternative Aquatics Limited | Warrington | 1998 |
| Alternative Capital Advisors Limited | Hampton | 2015 |
| Alternative Health Center Ltd | Haverfordwest | 2024 |
| Alternative Landfill Solutions Limited | Wolverhampton | 2013 |
| Alternative Networks Limited | Reading | 1998 |
| Alternative Norfolk Limited | Cromer | 2019 |
| Alternative Plans Limited | Daventry | 2022 |
| Alternewenergy Ltd | Cambridge | 2021 |
| Alternotion Limited | Wedmore | 2025 |
| Alteva Digital Limited | Waterlooville | 2019 |
| Altex Limited | Calne | 2006 |
| Althorp Estates Limited | Rowley Regis | 2023 |
| Althorp Nominee One Limited | Northampton | 2013 |
| Althorp Nominee Two Limited | Northampton | 2013 |
| Althorpe Properties Limited | Gloucestershire | 1979 |
| Altia Limited | Selby | 2018 |
| Altia-Abm Group Limited | Nottingham | 2017 |
| Alticare Ltd | Coventry | 2024 |
| Alticore Ltd | London | 2013 |
| Altis International Investments Ltd | London | 2015 |
| Altitude N I Ltd | Carryduff | 2015 |
| Altitude Aluminium Limited | Pulford | 2013 |
| Altitude INK Ltd | London | 2025 |
| Altitudeearth Ltd | London | 2019 |
| Altius General Trading Ltd | Manchester | 2026 |
| Altivery Ltd | Harrow | 2012 |
| Altivon Labs Ltd | Doncaster | 2026 |
| Alto Environmental Ltd | Peterborough | 2013 |
| Alto Executive Ltd | Cheltenham | 2012 |
| Alto International Ltd. | London | 2009 |
| Alto Kitchens Limited | Plymouth | 2013 |