| Armstrong Crayden Group Ltd | Construction | 2025 |
| Armtrack Group Limited | Wholesale & retail | 2018 |
| Armtrack Trading Limited | Wholesale & retail | 2012 |
| Arnold Marine Limited | Transport & logistics | 2025 |
| Aroma Coffees Ltd | Wholesale & retail | 2025 |
| Arquo Technologies Ltd | Information & communication | 2017 |
| Art & Science International Limited | Administrative & support | 2004 |
| Artemis Green Consulting Ltd | Professional & scientific | 2016 |
| Arten Limited | Administrative & support | 2013 |
| Arthas Group Limited | Financial services | 2021 |
| Article Seven Limited | Information & communication | 2006 |
| Artistry Brickwork Limited | Administrative & support | 2017 |
| Artwood Studios Ltd | Other services | 2024 |
| Arujah Ltd | Health & social care | 2025 |
| Arundel (Sidcup) Management Company Limited | Households | 1982 |
| ARX Electrical Contracting Ltd | Construction | 2025 |
| Ascott Electrical Services Ltd | Construction | 2018 |
| ASD Pro Build Ltd | Construction | 2014 |
| ASD UK Holdings Limited | Financial services | 2018 |
| ASD UK Properties Limited | Real estate | 2018 |
| Asel UK Packaging Ltd | Wholesale & retail | 2022 |
| ASH Court Burnt ASH Hill (Management) Limited | Households | 1987 |
| ASH Technical Consultancy Services Limited | Extraterritorial | 2013 |
| Ashbourne Development Ventures Limited | Construction | 2016 |
| Ashby Clearance and Recycling Limited | Water & waste | 2021 |
| Ashcroft Construction Group Ltd | Construction | 2023 |
| Ashimoomidashi Limited | Administrative & support | 2023 |
| Ashkuri Consultancy Limited | Professional & scientific | 2017 |
| Ashleigh Sade Homes Ltd | Real estate | 2019 |
| Ashly Court (Sidcup) Management Company Limited | Households | 1990 |
| Ashwood Plumbing Services Limited | Construction | 2019 |
| Ashworth Building Services Ltd | Construction | 2016 |
| ASK19 Holdings Limited | Financial services | 2020 |
| Askcruise Ltd | Information & communication | 2026 |
| Askona UK Ltd | Construction | 2013 |
| Aslan PCS Ltd | Professional & scientific | 2025 |
| ASP Removals & Storage Limited | Transport & logistics | 2018 |
| Aspect Lifts Ltd | Construction | 2003 |
| Aspire Heating Limited | Construction | 2017 |
| Aspire Plumbing & Heating Limited | Construction | 2010 |
| Aspire Plumbing and Drainage Limited | Administrative & support | 2017 |
| ASS Holdings Limited | Extraterritorial | 2008 |
| Assist.Cleaning Ltd | Administrative & support | 2015 |
| Association of Descendants of General Yang Hucheng's 38TH Army Overseas | Other services | 2023 |
| Astro Hydration Limited | Manufacturing | 2025 |
| Astute Training Consultancy Limited | Education | 2013 |
| ASW Plumbing Limited | Construction | 2019 |
| ATC Construction Services Limited | Construction | 2019 |
| ATH Catering (Bromley) Limited | Hospitality | 2023 |
| ATH Catering (Kent) Limited | Hospitality | 2017 |
| ATH Catering (Tonbridge) Limited | Professional & scientific | 2014 |
| ATH Catering (Tunbridge Wells) Limited | Professional & scientific | 2016 |
| ATH Catering Limited | Hospitality | 2012 |
| Athletes Kitchen UK Ltd | Hospitality | 2014 |
| Aticavo Textile Conservation Limited | Arts & recreation | 2022 |
| Atika Property Limited | Real estate | 2022 |
| Atkins Family Holdings Limited | Financial services | 2025 |
| Atlas Building Consultants Ltd | Construction | 2013 |
| Atlas Drone Solutions Ltd | Professional & scientific | 2018 |
| Atlas Global Property Group Limited | Construction | 2021 |
| Atlas Health Group Limited | Financial services | 2021 |
| Atlas New Co 0422 Limited | Health & social care | 2022 |
| Atlas Picturehouse Ltd | Information & communication | 2022 |
| ATM Groundworks Limited | Construction | 2016 |
| ATS Diamond Tools Limited | Wholesale & retail | 2011 |
| Attire Sourcing Ltd | Professional & scientific | 2022 |
| AU Scaffolding Ltd | Construction | 2021 |
| Auctus Ventures Ltd | Professional & scientific | 2018 |
| August 15 Limited | Financial services | 2017 |
| Aura Energy Solutions Limited | Professional & scientific | 2013 |
| Austen Lewis Limited | Administrative & support | 1985 |
| Autech Systems Limited | Administrative & support | 2016 |
| Authenticom Limited | Professional & scientific | 2020 |
| Autism Hampshire | Wholesale & retail | 1983 |
| Autowasche Ltd | Administrative & support | 2025 |
| AUX Delices DES Iles Cafe Ltd | Hospitality | 2018 |
| AV Broker Services Limited | Wholesale & retail | 2025 |
| AV Hair Design Limited | Other services | 2019 |
| AV Nails Ltd | Other services | 2023 |
| Avenues East | Health & social care | 1997 |
| Avenues London | Health & social care | 2009 |
| Avenues Management Services Limited | Health & social care | 2022 |
| Avenues South East | Health & social care | 2000 |
| Avery Hill Charitable Trust | Other services | 2004 |
| Aviary Homes Ltd | Financial services | 2020 |
| Avotech Limited | Construction | 2016 |
| AW Consult Ltd | Administrative & support | 2023 |
| AWB Solutions Limited | Other services | 2026 |
| AWD Rail Services Ltd | Administrative & support | 2013 |
| Axiom Audio Ltd | Manufacturing | 2021 |
| Axston Alliance Ltd | Real estate | 2026 |
| AXX Interiors Ltd | Construction | 2018 |
| Ay&Bo Ltd | Hospitality | 2022 |
| Ayec Ltd | Professional & scientific | 2021 |
| Ayla Wimpy Ltd | Hospitality | 2026 |
| Aylesford Scaffolding Limited | Construction | 2022 |
| Ayusha Personalised Nutrition Ltd | Health & social care | 2023 |
| Azurnyx Ltd | Administrative & support | 2020 |
| B & B Business Equipment Limited | Manufacturing | 1985 |
| B & C Developments South East Limited | Administrative & support | 2018 |