| Arcius Energy Egypt Limited | Mining & quarrying | 2024 |
| Ardshieling Limited | Information & communication | 2005 |
| Ariano's Limited | Hospitality | 2026 |
| Ariesan Ltd | Professional & scientific | 2016 |
| Ariyan Hotels Limited | Hospitality | 2015 |
| ARK34 Limited | Wholesale & retail | 2007 |
| Arkrule Limited | Construction | 2007 |
| Arlington Kitchens Limited | Construction | 2000 |
| Armada Maritime Cyber Security Systems Ltd | Information & communication | 2018 |
| Arod Enterprises Limited | Professional & scientific | 2006 |
| Aromair Limited | Manufacturing | 1999 |
| Arowra Events Management Ltd | Other services | 2022 |
| ARP Africa Travel Limited | Administrative & support | 1991 |
| Arran James Consulting Limited | Professional & scientific | 2004 |
| Arrow Builders Limited | Wholesale & retail | 1998 |
| Arrow Tech Ltd | Wholesale & retail | 2026 |
| Art Management Limited | Administrative & support | 2003 |
| Art-Ma Ltd | Wholesale & retail | 1999 |
| Arterberri Limited | Professional & scientific | 2006 |
| Articleboy Limited | Information & communication | 2021 |
| Articulate Analysis Ltd | Professional & scientific | 2013 |
| Arun Associates Limited | Professional & scientific | 1997 |
| Arun Karia & Co. Limited | Professional & scientific | 1995 |
| ARW Electrical Limited | Construction | 1997 |
| Aryan Enterprises Limited | Wholesale & retail | 2003 |
| Asal 60 Limited | Health & social care | 2012 |
| Ascend Professional Services Limited | Information & communication | 2013 |
| Ascendancy Media Limited | Information & communication | 2000 |
| ASD Healthcare Ltd | Wholesale & retail | 2020 |
| ASD Tradings Ltd | Wholesale & retail | 2023 |
| Asepsis Medical Legal Services Limited | Health & social care | 2006 |
| ASH TV Satellite Limited | Administrative & support | 2003 |
| Ashdoon Plant Hire Ltd | Construction | 2006 |
| Ashford Court (Edgware) Property Management Co. Limited | Households | 1966 |
| Ashford Truckstop Freehold Limited | Manufacturing | 2023 |
| Ashley Cleaning Services Limited | Administrative & support | 2000 |
| Ashleyd Limited | Other services | 2020 |
| Ashore Capital Ltd | Real estate | 2025 |
| Ashprint (London) Limited | Wholesale & retail | 2003 |
| Ashram Community Trust | Hospitality | 2003 |
| Ashtone Limited | Wholesale & retail | 1983 |
| Ashutosh Events Limited | Hospitality | 2006 |
| Ashwells Associates Limited | Professional & scientific | 2002 |
| Ashwells Limited | Professional & scientific | 2000 |
| ASI (Birkenhead) Ltd | Construction | 2018 |
| Asian Hiphop Festival Ltd | Arts & recreation | 2022 |
| Asian Media Limited | Professional & scientific | 1994 |
| ASK Godders Management Limited | Administrative & support | 2007 |
| ASK Properties Lettings Limited | Real estate | 2024 |
| Asli Baharan Punjab Diyan | Arts & recreation | 2000 |
| ASM Accounting Services Limited | Professional & scientific | 2002 |
| ASM Property Solutions Ltd | Construction | 1999 |
| Asnaf International Limited | Wholesale & retail | 1982 |
| Aspects of Wine Limited | Education | 2002 |
| Aspen Maine Consulting Limited | Professional & scientific | 1997 |
| Aspiration (UK) Limited | Construction | 2001 |
| Aspirax Ltd | Arts & recreation | 2026 |
| Aspire Mortgages & Financial Services Ltd | Financial services | 2007 |
| Aspley Court Limited | | 1984 |
| Aspm Consultancy Limited | Information & communication | 2014 |
| Asset Design and Build Limited | Construction | 2019 |
| Association for Solution Focus in Organisations Limited | Other services | 2016 |
| Astin Invest Ltd | Professional & scientific | 2012 |
| Astraseal Northwest Limited | | 1963 |
| Asurion Europe Limited | Financial services | 2008 |
| AT Effects Ltd | Arts & recreation | 2018 |
| ATD Electrical Limited | Manufacturing | 2005 |
| Athwal Associates Limited | Information & communication | 2006 |
| Atkinsons Residential Limited | Real estate | 2000 |
| Atlantic 2/3 UK Holdings Limited | Professional & scientific | 2000 |
| Atlantic Corporation Limited | Real estate | 2001 |
| Atlantis Diesels (UK) Limited | Wholesale & retail | 2007 |
| ATS Property Investments Limited | Real estate | 2024 |
| Atticus Productions Limited | Arts & recreation | 2010 |
| Atwi Properties Ltd | Real estate | 2023 |
| Audio Systems Limited | Information & communication | 1965 |
| Audio Visual Lifestyle Limited | Wholesale & retail | 2000 |
| Audley Scientific Limited | Manufacturing | 1986 |
| Audrey Property Group Ltd | Real estate | 2021 |
| Audrius Ltd | Construction | 2010 |
| Augmenture Limited | Professional & scientific | 2003 |
| AURA3 Ltd | Wholesale & retail | 2015 |
| Auromira Trust Limited | Other services | 1998 |
| Aurora Accountancy & Taxation Training Ltd | Education | 2006 |
| Aurvia Limited | Real estate | 2004 |
| Authentic Leadership Associates Ltd | Professional & scientific | 2006 |
| Authentics (U.K.) Limited | | 1990 |
| Autofleet Salvage Limited | Administrative & support | 2003 |
| Autoleaseplan Ltd | Financial services | 2004 |
| Autovend(Uk) Ltd | Other services | 2023 |
| AV Sales (Europe) Limited | Wholesale & retail | 2003 |
| Avalanche Cleaning Limited | Administrative & support | 2007 |
| Avenue Corporate Planning Limited | Professional & scientific | 2002 |
| AVG Associates Limited | Professional & scientific | 2007 |
| Avpm Engineering Ltd | Professional & scientific | 2021 |
| Avula Properties Limited | Real estate | 2006 |
| Awelcome Ltd | Health & social care | 2006 |
| Awesomebooks Limited | Professional & scientific | 2007 |
| Axivm Ltd | Education | 2024 |
| Axsar Technologies Limited | Information & communication | 2001 |