| African Conservation Experience Limited | Administrative & support | 1999 |
| Agenda Capital Partners 2 Limited | Real estate | 2012 |
| Agenda E1 Limited | Administrative & support | 2013 |
| Agenda E2 Limited | Real estate | 2013 |
| Agenda E3 Limited | Health & social care | 2013 |
| Agenda Homes Ltd | Construction | 2014 |
| Agentflux Ltd | Information & communication | 2025 |
| Agentic Computers Ltd | Wholesale & retail | 2025 |
| AGI Textiles Ltd | Wholesale & retail | 2017 |
| Agljh Limited | Manufacturing | 2025 |
| Agnian Ltd | Information & communication | 2006 |
| Agnieszka Fronc Ltd | Administrative & support | 2011 |
| Agri Power Solution Limited | Administrative & support | 2025 |
| Agrisource Limited | Extraterritorial | 2020 |
| Ahkmad TM Limited | Construction | 2026 |
| AHL Commercials Ltd | Wholesale & retail | 2023 |
| Ahwc Group Ltd | Information & communication | 2024 |
| AI 4 Work Ltd | Other services | 2024 |
| Aiblify Limited | Professional & scientific | 2021 |
| Aime Thai Ltd | Hospitality | 2014 |
| Aimstar Limited | Professional & scientific | 2024 |
| Ainscough Engineering Limited | Real estate | 2003 |
| Air & More Limited | Wholesale & retail | 2015 |
| Air Business Advisors Limited | Professional & scientific | 1999 |
| Air Shop 365 Limited | Wholesale & retail | 2021 |
| Airdesk Services Limited | Information & communication | 2018 |
| Airponix Seed UK Ltd | Agriculture & fishing | 2026 |
| Airspace Unlimited Ltd | Information & communication | 2018 |
| Airstickz Ltd | Manufacturing | 2025 |
| AJE IT Solutions Ltd | Information & communication | 2021 |
| Ajks Vintage Ltd | Wholesale & retail | 2016 |
| AJS Traffic Management Ltd | Construction | 2025 |
| AK Productions Limited | Information & communication | 2026 |
| Ak-Jk Cleaning Services Limited | Administrative & support | 2019 |
| Ak.Kickzz Ltd | Wholesale & retail | 2025 |
| AKC Capital Ltd | Financial services | 2025 |
| AKC Invest Ltd | Real estate | 2024 |
| Akobi Holdings Ltd | Construction | 2024 |
| Akorro Studio Limited | Information & communication | 2026 |
| Aktivedge Solutions Limited | Financial services | 2017 |
| AL Best Construction Limited | Construction | 2026 |
| AL Khaime Ltd | Real estate | 2025 |
| AL Zeinab Limited | Other services | 2017 |
| Alan Rides Company (ARC) Ltd | Wholesale & retail | 2019 |
| Alandac Limited | Professional & scientific | 2025 |
| ALB Bar Group Ltd | Hospitality | 2026 |
| Albany Court (Ferrymoor) Limited | Households | 1972 |
| Albert Development Limited | Real estate | 2017 |
| Albert Hall Dance Floors Ltd | Administrative & support | 1998 |
| Albertine Holdings Ltd | Hospitality | 2021 |
| Albion Care Ltd | Health & social care | 2013 |
| Albion Property (UK) Limited | Financial services | 2001 |
| Alconbury Capital Ltd | Professional & scientific | 2025 |
| Alconbury Operations Ltd | Professional & scientific | 2025 |
| Aldermanbury Trade Limited | Construction | 2008 |
| Alehunters Ltd | Administrative & support | 2018 |
| Alemi Ltd | Information & communication | 2024 |
| Alessio Gessa Ltd | Health & social care | 2023 |
| Alex DRY Cleaner's Ltd | Other services | 2025 |
| Alex Drycleaning Limited | Other services | 2015 |
| Alexacarter Ltd | Professional & scientific | 2024 |
| Alexander James Capital Ltd | Financial services | 2023 |
| Alexander Marcar and Company Limited | Professional & scientific | 1956 |
| Alexis Amor Ltd | Wholesale & retail | 2005 |
| Alfa Consultancy Ltd | Administrative & support | 2018 |
| Alfie Gibbs Deal Sourcing Ltd | Administrative & support | 2025 |
| Alfresco Adventures Limited | Arts & recreation | 2012 |
| Algar Road Limited | Real estate | 2021 |
| Alie Properties Ltd | Construction | 2022 |
| Align Education Limited | Education | 2014 |
| Align Partners Ltd | Real estate | 2018 |
| Align Systems Ltd | Information & communication | 2026 |
| Aligned (MC) Ltd | Other services | 2026 |
| Alison Cardy Ltd | Information & communication | 2018 |
| ALL 4 Construction Limited | Construction | 2023 |
| ALL Hardware Ltd | Wholesale & retail | 2025 |
| ALL Ride NOW LLP | | 2014 |
| ALL Things Padel Limited | Construction | 2024 |
| ALL Things Well Limited | Wholesale & retail | 2021 |
| Allam Logistics Ltd | Transport & logistics | 2019 |
| Allan Richardson Commercial Vehicle Engineers Limited | Wholesale & retail | 2004 |
| Alldus International Consulting Limited | Administrative & support | 2020 |
| Alliance Travel Holdings Ltd | Financial services | 2016 |
| Allibone Consulting Limited | Real estate | 2012 |
| Allied Crowds Limited | Information & communication | 2014 |
| Allocate Bidco Limited | Information & communication | 2014 |
| Allocate Software Limited | Information & communication | 1993 |
| Almatext Ltd | Administrative & support | 2020 |
| Alohomora Consultants Ltd | Administrative & support | 2025 |
| Aloysius WB Limited | Professional & scientific | 2017 |
| Alpha Building Consultants Limited | Professional & scientific | 2024 |
| Alpha Building Control Limited | Construction | 2018 |
| Alpha Centauri Group Limited | Real estate | 2016 |
| Alpha LA Roche Limited | Wholesale & retail | 2013 |
| Alpha Strategy Ltd | Professional & scientific | 2026 |
| Alpha Tech Capital Ltd | Professional & scientific | 2018 |
| Alpharise Software Limited | Information & communication | 2024 |
| Alphasenti Limited | Information & communication | 2018 |
| Alpine Capital Consultants Ltd | Professional & scientific | 2020 |
| Alpine Fintech UK Ltd | Wholesale & retail | 2021 |