| Anav Limited | Wholesale & retail | 2020 |
| Anayasd Limited | Information & communication | 2015 |
| Anbo Textiles Limited | Wholesale & retail | 1977 |
| AND Techno Solutions Ltd | Financial services | 2024 |
| Andante Advisory Limited | Professional & scientific | 2022 |
| Andy J Hague Limited | Information & communication | 2010 |
| Angellinx Ltd | Administrative & support | 2025 |
| Anglersnake Software Solutions Limited | Information & communication | 2021 |
| Anglo Chesham Management Limited | Real estate | 2004 |
| Angus Pond Architects Limited | Professional & scientific | 2002 |
| Anjay Services Ltd | Professional & scientific | 2024 |
| Anna Victoria Properties Limited | Real estate | 2021 |
| Annika K Consultancy Ltd | Professional & scientific | 2024 |
| Annika K Developments Ltd | Real estate | 2020 |
| Annys Hamilton Ltd | Information & communication | 2021 |
| Anorak Consulting Limited | Professional & scientific | 2014 |
| Another Angle Ltd | Professional & scientific | 2010 |
| Antron Security Limited | Administrative & support | 1994 |
| Apalondon Property Limited | Real estate | 2015 |
| Apex Building and Roofing Limited | Construction | 2013 |
| Apexdrives Ltd | Transport & logistics | 2025 |
| Apollonia Limited | Professional & scientific | 2006 |
| Appletree Cottage Consulting Limited | Professional & scientific | 2011 |
| Applied Healthcare Academy Ltd | Information & communication | 2018 |
| Apprenteskills Ltd | Education | 2026 |
| APS + Sons Ltd | Real estate | 2013 |
| Aqua Healthcare Ltd | Administrative & support | 2018 |
| Aquavalet Limited | Other services | 2016 |
| AR Health and Wellbeing Ltd | Other services | 2024 |
| AR18 Limited | Manufacturing | 2003 |
| AR8 Support Services Ltd | Information & communication | 2026 |
| Archies Gallery Limited | Other services | 2019 |
| Ardesey Ltd | Professional & scientific | 2019 |
| Arhato Limited | Information & communication | 2019 |
| ARK Corporation (U.K.) Co Ltd | Other services | 2011 |
| Armourtec Ltd | Construction | 2015 |
| Armyne Ltd | Other services | 2020 |
| Arneway Ltd | Professional & scientific | 2017 |
| Arnik Solutions Limited | Professional & scientific | 2017 |
| Art of Your Success Ltd | Wholesale & retail | 2025 |
| Artemis Tree Services Limited | Agriculture & fishing | 2006 |
| Arti Maru Limited | Professional & scientific | 2023 |
| Artline Joinery Ltd | Manufacturing | 2014 |
| Arvy Consultancy (UK) Limited | Information & communication | 2013 |
| Arvyden UK Ltd | Wholesale & retail | 2023 |
| Arya LDN Limited | Wholesale & retail | 2024 |
| Arycay Community Services Ltd | Transport & logistics | 2022 |
| AS Chiltern Homecare Ltd | Health & social care | 2015 |
| ASA Consulting Services Ltd | Administrative & support | 2019 |
| Asaph Solutions Limited | Professional & scientific | 2002 |
| ASB Plumbing and Heating Supplies Ltd | Wholesale & retail | 2022 |
| Ascent AK Property Ltd | Real estate | 2023 |
| Ascot Healthcare Services Limited | Other services | 2013 |
| Asesu Ltd | Professional & scientific | 2022 |
| Asferica Consulting Limited | Professional & scientific | 2011 |
| ASH Mann Ltd | Real estate | 2009 |
| Ashdown Place RTM Company Ltd | Real estate | 2010 |
| Asheridge Management Limited | Professional & scientific | 2001 |
| Ashok Pattni Limited | Information & communication | 2014 |
| Ashurst Ventures Limited | Construction | 2025 |
| Ashward Estates Ltd | Real estate | 2026 |
| Askew Hawkins Limited | Real estate | 2003 |
| ASM Consultancy Services Ltd | Information & communication | 2016 |
| Aspect Apartments Limited | Households | 2012 |
| Aspis SC Ltd | Professional & scientific | 2022 |
| Astec Properties (Church Street) Ltd | Real estate | 2013 |
| Astec Properties (Midland Road) Ltd | Real estate | 2012 |
| Astec Properties Ltd | Real estate | 2008 |
| ATB Agency Services Limited | Professional & scientific | 2009 |
| Athena FM Services Ltd | Professional & scientific | 2011 |
| Atlas Green Global Ltd | Administrative & support | 2026 |
| Atlas Latimer Limited | Real estate | 2022 |
| Atomic Motor Company Ltd | Wholesale & retail | 2019 |
| Atri Advisory Limited | Professional & scientific | 2003 |
| Atrio Solutions Limited | Construction | 2019 |
| Attomus Limited | Information & communication | 2008 |
| Augmentra AI Ltd | Information & communication | 2025 |
| Aura Virtual Office Limited | Administrative & support | 2026 |
| Aureate Consulting Ltd | Professional & scientific | 2026 |
| Aurelian Financial Planning Ltd | Professional & scientific | 2025 |
| Aurialogic Limited | Transport & logistics | 2016 |
| Authentico.Life Ltd | Information & communication | 2025 |
| Auto Prestige London Ltd | Wholesale & retail | 2018 |
| Auto Revive London Limited | Wholesale & retail | 2010 |
| Auto Skills CRS Limited | Manufacturing | 2024 |
| Auto Trade Spot Limited | Wholesale & retail | 2025 |
| Autobodyworx Limited | Wholesale & retail | 2003 |
| Autotech Centre Garage Ltd | Wholesale & retail | 2021 |
| Autoventure Ltd | Wholesale & retail | 2025 |
| AV Custom Electrical Ltd | Construction | 2023 |
| AV Custom Ltd | Information & communication | 2015 |
| Avas Medical Ltd | Health & social care | 2016 |
| Avenue House (Chesham) Management Limited | Households | 1978 |
| Aver Logistics Ltd | Transport & logistics | 2017 |
| Avesh Construction Limited | Real estate | 2019 |
| Aviation Checklist Ltd | Information & communication | 2020 |
| Avondale Financial Ltd | Financial services | 1997 |
| AW Aviation Consultancy Services Limited | Transport & logistics | 2015 |
| Axion Advisory Ltd | Professional & scientific | 2025 |
| Axis Accountancy Ltd | Professional & scientific | 2026 |