| ALL Star Shakes Limited | Hospitality | 2022 |
| Allen Bespoke Metal Ltd | Manufacturing | 2025 |
| Allen Farms Limited | Agriculture & fishing | 1960 |
| ALM Sheet Metal and Fabrication Ltd | Manufacturing | 2022 |
| Alpha Chiropractic Health Clinic Ltd | Health & social care | 2018 |
| Alpha Edge Ltd | Information & communication | 2018 |
| Alpha Flow Limited | Wholesale & retail | 2008 |
| Alpha Innovare Limited | Information & communication | 2018 |
| Alpha Intrinsic Ltd | Professional & scientific | 2023 |
| Alternative Real Estate Investments Limited | Information & communication | 2019 |
| Alura Candles Limited | Professional & scientific | 2001 |
| AM Transforma Consulting Limited | Professional & scientific | 2025 |
| Amaxim Consulting Ltd | Information & communication | 2016 |
| Amjos (Herts) Ltd | Health & social care | 2022 |
| AML Venture Ltd | Financial services | 2021 |
| Amorpho IT Services Ltd | Information & communication | 2023 |
| Amra Media Solutions Limited | Information & communication | 2003 |
| Amworth Solutions Limited | Professional & scientific | 2026 |
| AMY Kilpin Ltd. | Professional & scientific | 2014 |
| AMZ Marketing Consulting Limited | Information & communication | 2019 |
| Anadelta Ltd | Information & communication | 2019 |
| Analysis Marketing Limited | Professional & scientific | 2008 |
| Analytique Limited | Professional & scientific | 2025 |
| AND SO SHE Awoke Limited | Wholesale & retail | 2020 |
| Angiel Consulting Ltd | Information & communication | 2025 |
| Anglican Methodist Association (Berkhamsted) Limited | Other services | 1980 |
| Anglo-Dutch Limited | Professional & scientific | 2002 |
| Ankh International Ltd | Wholesale & retail | 2024 |
| Anvil Resourcing Solutions Ltd | Professional & scientific | 2022 |
| AO Contracting Ltd | Information & communication | 2021 |
| AOB Designs Ltd | Construction | 2023 |
| Apps to Life Limited | Information & communication | 2013 |
| Apsk Consultancy Ltd | Information & communication | 2020 |
| Aquila Commodities Limited | Professional & scientific | 2012 |
| ARC of London Ltd | Information & communication | 2024 |
| Arcane Technology Limited | Administrative & support | 2007 |
| Archimagic Ltd | Information & communication | 2026 |
| Architechsure Limited | Information & communication | 2025 |
| Archway Court Consultants Limited | Administrative & support | 2011 |
| Arctos Limited | Professional & scientific | 2013 |
| Ardmore Consult Ltd | Professional & scientific | 2023 |
| Arena Interiors Limited | Construction | 1989 |
| ARG Scenic Services Ltd | Information & communication | 2013 |
| Argan Media Limited | Information & communication | 2020 |
| Argaux Ltd | Wholesale & retail | 2017 |
| Aries Assets Limited | Real estate | 2024 |
| ARL Flight Training Ltd | Education | 2022 |
| Arnaud Security Systems Ltd | Construction | 2023 |
| Arniko Ltd | Information & communication | 2018 |
| ARP Consulting Limited | Information & communication | 2018 |
| Arran IT Consultancy Ltd | Information & communication | 2023 |
| Artilda Consulting Limited | Information & communication | 2018 |
| Artisan Bar & Restaurant Ltd | Hospitality | 2021 |
| AS Accounting Solutions Ltd | Professional & scientific | 2005 |
| AS Sound AS a Bell Ltd | Real estate | 2025 |
| Aseptic Connectors Limited | Manufacturing | 2018 |
| ASH Information Systems Limited | Information & communication | 1995 |
| ASH Security Limited | Administrative & support | 2018 |
| ASH Taylor Ltd | Information & communication | 2018 |
| Ashley Paving Limited | Construction | 2005 |
| Ashmore Solutions Ltd | Real estate | 2025 |
| Ashridge Care Ltd | Education | 2013 |
| Ashridge Property Investments Limited | Real estate | 2019 |
| Ashridge Property Ltd | Real estate | 2020 |
| Ashton Consult Ltd | Construction | 2024 |
| Asset and Property FX Limited | Financial services | 2008 |
| Associated Dynamics Systems Limited | Information & communication | 1987 |
| Assured Surveying & Design Limited | Professional & scientific | 2015 |
| Asterope Life Sciences Ltd | Professional & scientific | 2025 |
| Aston Clinton Cosy Conversions Ltd | Construction | 2025 |
| Astraevitas Ltd | Professional & scientific | 2024 |
| Astrope Properties Limited | Real estate | 2017 |
| Astus Solutions Limited | Information & communication | 2023 |
| Astute Analytics Limited | Professional & scientific | 2011 |
| AT M Enterprisers Ltd | Wholesale & retail | 2023 |
| Athena Business Services Ltd | Professional & scientific | 2022 |
| Athena Worldwide Solutions Ltd | Information & communication | 2022 |
| Atlin Analytics Ltd | Professional & scientific | 2019 |
| Attanasio Design and Development Limited | Professional & scientific | 2018 |
| Attollo Project Management Ltd | Professional & scientific | 2007 |
| Audit Risk Partners Limited | Professional & scientific | 2011 |
| Aurora Audio Visual Limited | Professional & scientific | 2009 |
| Automotive Transformations Ltd | Professional & scientific | 2024 |
| AV Morgans Limited | Hospitality | 2015 |
| Avalon Insights Limited | Professional & scientific | 2024 |
| Avandra Consulting Ltd | Professional & scientific | 2024 |
| AVE Integrations Limited | Information & communication | 2008 |
| Aviation Structures Services Ltd | Manufacturing | 2020 |
| Aviz Digital Ltd | Information & communication | 2019 |
| AVN Advisory Limited | Professional & scientific | 2017 |
| Awaken Communications Ltd | Professional & scientific | 2012 |
| Axon Black Ltd | Administrative & support | 2023 |
| Aydin Best Foods Ltd | Hospitality | 2021 |
| Ayla Engineering Ltd | Construction | 2022 |
| Aylesbury Truck Hire Ltd | Administrative & support | 2018 |
| Azrooh Ltd | Health & social care | 2009 |
| B COX Landscaping & Driveways Ltd | Administrative & support | 2024 |
| B.A.S Flooring Ltd | Construction | 2024 |
| Back on Track (GB) Ltd | Arts & recreation | 2010 |
| Backtrace Ltd | Information & communication | 2018 |