| Almoro Ltd | Professional & scientific | 2025 |
| Almost Anime Limited | Information & communication | 2019 |
| Almsford Media Limited | Information & communication | 2019 |
| Almucantar Limited | Information & communication | 2009 |
| Alpha Lupi Consulting Ltd | Information & communication | 2003 |
| Alphabet Properties Limited | Construction | 2003 |
| Alpine Controls Limited | Construction | 2025 |
| Alpine Worldwide Group Ltd | Wholesale & retail | 2025 |
| Alpine Worldwide Ltd | Wholesale & retail | 2019 |
| ALS Home Improvement Ltd | Construction | 2018 |
| ALT Consulting Limited | Information & communication | 2011 |
| Alter Services Ltd | Professional & scientific | 2018 |
| Alterscope Ltd | Information & communication | 2022 |
| Altimise Ltd | Professional & scientific | 2017 |
| Altosig Limited | Transport & logistics | 2003 |
| Altura Padel Sports Ltd | Arts & recreation | 2025 |
| Aluminium Window Systems Limited | Manufacturing | 2024 |
| AM Empire (UK) Limited | Real estate | 2002 |
| AM Machine Tools and Servicing Ltd | Manufacturing | 2024 |
| AM Truck & Coach Ltd | Wholesale & retail | 2007 |
| Amalco Ltd | Professional & scientific | 2020 |
| Amazing Fences and Landscaping Ltd | Other services | 2026 |
| Amber GLO Limited | Construction | 2006 |
| Amber Safety Consulting Limited | Professional & scientific | 2019 |
| Amdb Consulting Ltd | Information & communication | 2024 |
| Amelia Gough Consultancy Ltd | Administrative & support | 2023 |
| Amelia Hepworth Landscape & Garden Design Limited | Professional & scientific | 2024 |
| Amellica Limited | Agriculture & fishing | 2015 |
| American Amusements (Wokingham) Limited | Arts & recreation | 2016 |
| American Amusements Holdings Limited | Arts & recreation | 1993 |
| AMF Genai Limited | Information & communication | 2025 |
| Amfem Estates Ltd | Real estate | 2025 |
| Ample Electrics Ltd | Construction | 2022 |
| Amrock Properties Limited | Real estate | 2017 |
| AMS (Doonans) Ltd | Manufacturing | 2023 |
| AMS Communications Ltd | Financial services | 2019 |
| AMS NVH Limited | Professional & scientific | 2026 |
| Amtek Electronic Solutions Ltd | Professional & scientific | 1999 |
| Amtek Engineering Group Limited | Professional & scientific | 2003 |
| Amtek Engineering Solutions Ltd | Professional & scientific | 2000 |
| Amtek Group Limited | Financial services | 2024 |
| Amtek Holdings Limited | Professional & scientific | 2022 |
| Amtek Technical Resources Limited | Professional & scientific | 2003 |
| AN Cloud Consultants Ltd | Professional & scientific | 2013 |
| An-Ve Designer Limited | Professional & scientific | 2024 |
| Analytical Data Ltd | Financial services | 2022 |
| ANALYTICS2INSIGHTS Limited | Information & communication | 2021 |
| Anastasia Fomitch Ltd | Professional & scientific | 2015 |
| Anbolu Limited | Information & communication | 2026 |
| Ancleggan 01 Limited | Energy | 2025 |
| Ancleggan 02 Limited | Energy | 2025 |
| Ancleggan Limited | Energy | 2020 |
| Anderton Consulting Ltd | Administrative & support | 2013 |
| Andrea Josse Project Management Limited | Professional & scientific | 2025 |
| Andres Leon Limited | Information & communication | 2019 |
| Andrew Coombs (GAS Engineer) Limited | Construction | 2008 |
| Andrew David Associates 2026 Limited | Financial services | 2025 |
| Andrew Hartwell Holdings Limited | Professional & scientific | 1998 |
| Andrew Ridley Advisory & Consulting Limited | Professional & scientific | 2023 |
| Andrew Waller Ltd | Wholesale & retail | 2016 |
| Aneil Karia Ltd | Information & communication | 2025 |
| ANF Upholstery Limited | Wholesale & retail | 2020 |
| Angelou Consulting Limited | Information & communication | 2023 |
| Angelus Properties Ltd | Real estate | 2023 |
| Angharad Cooper Consultancy and Coaching Limited | Professional & scientific | 2021 |
| Anglian Software Ltd | Information & communication | 2017 |
| Anglo Baiter Management Limited | Households | 2002 |
| Animated Ltd | Information & communication | 2018 |
| Anjin Projects Ltd | Administrative & support | 2024 |
| Anneroy Property Ltd | Real estate | 2017 |
| Antanas Consulting Ltd | Information & communication | 2016 |
| Antarctic Group Limited | Information & communication | 2024 |
| Antelao Holding Limited | Professional & scientific | 2020 |
| Antell Brothers Limited | Agriculture & fishing | 1955 |
| Anthony Robinson Industries Limited | Professional & scientific | 2025 |
| Anthysa Limited | Professional & scientific | 2024 |
| Antimatter Limited | Information & communication | 2016 |
| Antipodes Import Co. Ltd | Wholesale & retail | 2017 |
| Anton Clarke Ltd | Professional & scientific | 2016 |
| Anwar Consulting Limited | Information & communication | 2024 |
| ANY Road Coaching Limited | Professional & scientific | 2024 |
| Anythingsa Limited | Wholesale & retail | 2020 |
| Aonia Consulting Limited | Professional & scientific | 2019 |
| AOW Carpentry Ltd | Extraterritorial | 2020 |
| Aoyama Limited | Information & communication | 2018 |
| AP Commercial Finance Limited | Financial services | 2021 |
| AP Kryza Ltd | Information & communication | 2026 |
| AP Mortgages Limited | Financial services | 2021 |
| AP Software Limited | Information & communication | 2016 |
| Apac Properties Limited | Administrative & support | 2017 |
| Apanarese Limited | Real estate | 2020 |
| Apeks Solutions Ltd | Information & communication | 2022 |
| Apex Finance Consultancy Ltd | Professional & scientific | 2024 |
| APL Cyber Limited | Information & communication | 2023 |
| Apmco Ltd | Professional & scientific | 2021 |
| Apperoso Ltd | Information & communication | 2017 |
| Applied CAE Limited | Professional & scientific | 2022 |
| Apps Consulting Limited | Information & communication | 2012 |
| Appt Design Limited | Information & communication | 2015 |
| Apptractor Development Ltd | Information & communication | 2026 |