| Atlas E.D.A. Property Services Limited | Construction | 2019 |
| Atlas Gardens Limited | Administrative & support | 2011 |
| Atlas Insulation Products Limited | Construction | 2015 |
| Atlas Medical Limited | Manufacturing | 2008 |
| Atlas Plant Hire Limited | Manufacturing | 2015 |
| Atlas Sourcing (Asia Pacific) Co., Limited | Extraterritorial | 2014 |
| Atlas Tree Surgery Limited | Agriculture & fishing | 2007 |
| Atlin Seating Limited | Other services | 2015 |
| Atmanic Ltd | Information & communication | 2025 |
| Atmo Bidco UK Limited | Financial services | 2023 |
| Atmo Consulting Ltd | Information & communication | 2020 |
| Atomjet Limited | Professional & scientific | 2010 |
| Atomsparq Ltd | Information & communication | 2026 |
| Atomsun Dynamics Ltd | Health & social care | 2022 |
| Atoz Sourcing Ltd | Extraterritorial | 2014 |
| Atria Court Management Company Limited | Real estate | 2007 |
| ATS Advisory Ltd | Professional & scientific | 2024 |
| Attainip Limited | Information & communication | 2025 |
| Attewater House Management Limited | Households | 2020 |
| Attica & Aspriter Ltd | Wholesale & retail | 2022 |
| Attocore Limited | Information & communication | 2014 |
| Attosphere Limited | Professional & scientific | 2019 |
| Atts(Uk) Ltd | Professional & scientific | 2016 |
| Attune Accountants Limited | Professional & scientific | 2020 |
| Attune Advisory (Cambridge) Limited | Extraterritorial | 2026 |
| Attune Plastic Surgery & Cosmetics Limited | Health & social care | 2013 |
| AU Aviation Ltd | Manufacturing | 2026 |
| Aubade Productions Ltd | Information & communication | 2025 |
| Aubay UK Limited | Information & communication | 2013 |
| Aucto Limited | Wholesale & retail | 2023 |
| Audi-Specialists.Co.Uk Limited | Wholesale & retail | 2005 |
| Audinate Ltd | Information & communication | 2010 |
| Audio First Designs Ltd | Wholesale & retail | 2024 |
| Audioforce Limited | Extraterritorial | 2007 |
| Audiotelligence Limited | Professional & scientific | 2017 |
| Audrey Arts Limited | Wholesale & retail | 2018 |
| Aufiss International Industries Limited | Extraterritorial | 2015 |
| Augmentra Limited | Information & communication | 2006 |
| August Clothing Limited | Wholesale & retail | 2025 |
| Aula (2) Limited | Financial services | 2013 |
| Aula Hospitality Limited | Hospitality | 2008 |
| Aula Property Partnership II LLP | | 2019 |
| Aula Property Partnership III LLP | | 2023 |
| Aula Property Partnership LLP | | 2017 |
| Aunty Pam's Kitchen Limited | Hospitality | 2020 |
| Aura 4 (Cambridge) Management Company Limited | Households | 2021 |
| Aura Henna Ltd | Other services | 2026 |
| Aura Lasers Ltd | Wholesale & retail | 2024 |
| Aura Medical Lasers Ltd | Wholesale & retail | 2026 |
| Aura Technical Solutions Ltd | Information & communication | 2011 |
| Auralis Aero Ltd | Professional & scientific | 2026 |
| Aurantius Financial Planning Ltd | Financial services | 2024 |
| Auravie Ltd | Wholesale & retail | 2025 |
| Aurea Nutrition Ltd | Health & social care | 2026 |
| Aurelia Patisserie Ltd | Manufacturing | 2020 |
| Aurex Capital Ltd | Professional & scientific | 2025 |
| Aurexia Limited | Professional & scientific | 2014 |
| Auri Potash (Netherland) Ltd | Wholesale & retail | 2023 |
| Aurion Roofing & Solar Solutions Ltd | Construction | 2025 |
| Auriplex Limited | Information & communication | 2005 |
| Aurora Isla Ltd | Wholesale & retail | 2025 |
| Aurora Text Solutions Ltd | Professional & scientific | 2021 |
| Aurora's Products Ltd | Wholesale & retail | 2020 |
| Auroratree Trading Ltd | Wholesale & retail | 2025 |
| Aursy Trade Ltd | Wholesale & retail | 2025 |
| Aurum & Sons Ltd | Wholesale & retail | 2025 |
| Ausra Software Limited | Information & communication | 1998 |
| Aussivin Technology Co., Ltd | Extraterritorial | 2021 |
| Austin Court (Cambridge) Management Company Limited | Households | 2014 |
| Austin Macauley Limited | Information & communication | 2018 |
| Austin Towers Ltd | Real estate | 2018 |
| Austin Tree Care Ltd | Agriculture & fishing | 2020 |
| Australia Deman Group Limited | Wholesale & retail | 2025 |
| Australia Olanwo Import and Export Group Co., Ltd | Mining & quarrying | 2024 |
| Australia Varo International Biotechnology Limited | Wholesale & retail | 2024 |
| Australian Pearl Company Ltd | Wholesale & retail | 2017 |
| Authentic Neapolitan Ltd | Hospitality | 2026 |
| Authenticard Ltd | Wholesale & retail | 2011 |
| Author Enterprises Ltd | Information & communication | 2017 |
| Authoripay Ltd | Administrative & support | 2019 |
| Autism Centre of Excellence | Professional & scientific | 2020 |
| Auto Caier Trading Co., Ltd | Extraterritorial | 2023 |
| Auto IC Limited | Information & communication | 2025 |
| Auto Rickshaw Limited | Hospitality | 2024 |
| Auto Speed Auto Parts Co., Ltd | Wholesale & retail | 2020 |
| Auto Town Limited | Wholesale & retail | 2023 |
| Autofina Limited | Professional & scientific | 2013 |
| Autohaem Ltd | Manufacturing | 2023 |
| Autohp Ltd | Wholesale & retail | 2023 |
| Automated Measurement Systems Limited | Information & communication | 1994 |
| Automatic Ltd | Information & communication | 2016 |
| Automatic Works Ltd | Information & communication | 2025 |
| Automation Simplified Ltd | Information & communication | 2025 |
| Automation Systems Commissioning Ltd | Construction | 2023 |
| Automations for Coaches Limited | Extraterritorial | 1993 |
| Automotiveworksolutions Ltd | Manufacturing | 2024 |
| Auton SOL Ltd | Administrative & support | 2026 |
| Autonomy Works Limited | Information & communication | 2026 |
| Autosonal Industry Co., Ltd | Extraterritorial | 2019 |
| Autostore Europe Ltd | Wholesale & retail | 2012 |