| Amprozone Ltd | Information & communication | 2024 |
| Amulet Private Office Limited | Financial services | 2016 |
| Analan LLP | | 2006 |
| Ananta Technologies Limited | Information & communication | 2011 |
| ANC Kitchen Limited | Hospitality | 2024 |
| Ancaster Butchers Limited | Wholesale & retail | 2010 |
| Ancaster Convenience Store Ltd | Wholesale & retail | 2024 |
| Ancaster Copper Hill Stone Limited | Mining & quarrying | 2004 |
| Ancaster Stratigraphic Services Ltd | Professional & scientific | 2010 |
| Anderson Equipment Ltd | Manufacturing | 2025 |
| Andorman (UK) Limited | Financial services | 2014 |
| Andrew Barraclough Limited | Information & communication | 2008 |
| Andrew Pile Limited | Professional & scientific | 2008 |
| Andrew Smith Property Developments Limited | Construction | 2014 |
| Andrews Environmental Consultancy Limited | Professional & scientific | 2020 |
| Angel MED Ltd | Manufacturing | 2001 |
| Angel Wells Ltd | Professional & scientific | 2026 |
| Angelos Coffee Limited | Wholesale & retail | 2020 |
| Angus DOW Limited | Arts & recreation | 2008 |
| Ani-Care Limited | Extraterritorial | 2011 |
| Animal Health Distributors Association (United Kingdom) Limited(The) | Other services | 1985 |
| Anisha Underwriting Limited | Financial services | 2009 |
| Annapurna Holdings Limited | Financial services | 2018 |
| Annick Ltd | Wholesale & retail | 2024 |
| Ansara Property Limited | Real estate | 2017 |
| Antal Repair Services Limited | Administrative & support | 2023 |
| Antalya Garden Ltd | Hospitality | 2025 |
| Antezz Blgh Ltd | Other services | 2024 |
| Anvi Cloud Services Limited | Information & communication | 2024 |
| AP Management Ltd | Real estate | 2025 |
| Apex Mobile Mechanics Ltd | Wholesale & retail | 2026 |
| APM R2R Ltd | Real estate | 2025 |
| Apple Green Media Ltd | Information & communication | 2014 |
| Apple Machinery Ltd | Manufacturing | 2018 |
| Apple Paper Sales Limited | Manufacturing | 2019 |
| Appleby Estate Management Ltd | Households | 2021 |
| Appletree Corner Daycare and Pre-School Ltd | Education | 2012 |
| Applied Energy Consultants Limited | Professional & scientific | 2020 |
| Applied Renewable Energy Limited | Professional & scientific | 2009 |
| APS Data Solutions Ltd | Information & communication | 2016 |
| Aqua Concepts East Midlands Ltd | Wholesale & retail | 2016 |
| Aquatherma Renewables Ltd | Construction | 2023 |
| Aquatic Chalks Ltd | Agriculture & fishing | 2000 |
| Aquisense Technologies (Europe) Limited | Wholesale & retail | 2015 |
| Arable Farm Contractors Limited | Agriculture & fishing | 2016 |
| Arap Limited | Hospitality | 2026 |
| ARC Groundworks (Lincs) Limited | Construction | 2025 |
| Archimedes Partners EOT Trustees Limited | Professional & scientific | 2024 |
| Archimedes Partners Limited | Financial services | 2012 |
| Architectural Bronze Limited | Manufacturing | 2014 |
| Architettura Limited | Construction | 2009 |
| ARE Logistics Limited | Transport & logistics | 2016 |
| Arete Advisors Ltd | Professional & scientific | 2024 |
| Argentum Kitchens Ltd | Professional & scientific | 2024 |
| Arhipro Glazing Ltd | Construction | 2026 |
| Arif Medico Ltd | Health & social care | 2026 |
| Armstrong & Holmes Limited | Manufacturing | 1977 |
| Arnica Online Ltd | Information & communication | 1995 |
| Arraquip Holdings Limited | Other services | 2016 |
| Arraquip Limited | Manufacturing | 1978 |
| Arraquip Steelstock Limited | Manufacturing | 1978 |
| ARS Group Ltd | Wholesale & retail | 2018 |
| Artemis Pursuit Ltd | Professional & scientific | 2026 |
| Artemisnature CIC | Health & social care | 2025 |
| Arthur Hudson Site Engineers Limited | Manufacturing | 2006 |
| Arthur Raymond & Co Limited | Professional & scientific | 2023 |
| Artworkzdesigns Ltd | Professional & scientific | 2021 |
| Asap Crash Repair Center Ltd | Wholesale & retail | 2013 |
| Ashaunea Ltd | Wholesale & retail | 2021 |
| Ashby Energy Assessors Limited | Professional & scientific | 2013 |
| Asher Swimpool Centre Limited | Construction | 1980 |
| Ashwood Land & Property Limited | Administrative & support | 1998 |
| Asian Noodle 51 Limited | Hospitality | 2023 |
| ASK Underwriting Limited | Financial services | 2009 |
| Asmm Brown Ltd | Construction | 2021 |
| Aspect Music Limited | Information & communication | 2018 |
| Asset X Ltd | Financial services | 2025 |
| Assistant Services Ltd | Households | 2024 |
| Association of Aesthetics Injectable Cosmetics Limited | Other services | 2012 |
| Association of Fundraising Consultants and Freelancers | Other services | 1992 |
| Astill & SON Services Limited | Manufacturing | 2016 |
| Astta Ltd | Arts & recreation | 2014 |
| AT in Sensu Ltd | Other services | 2017 |
| Atelier Homes Ltd | Real estate | 2026 |
| Atepa Properties Limited | Real estate | 2004 |
| Athena Strategic Consulting Ltd | Professional & scientific | 2015 |
| Athonish Ltd | Wholesale & retail | 2021 |
| Attention 2 Care Limited | Health & social care | 2020 |
| Atticus Building Consultants Limited | Professional & scientific | 2010 |
| Attis Partnership Limited | Professional & scientific | 2020 |
| AUK Gym Ltd | Arts & recreation | 2020 |
| Auremont Ltd | Wholesale & retail | 2026 |
| Aurora Accountancy Services Ltd | Professional & scientific | 2024 |
| Auto Picasso Limited | Wholesale & retail | 2026 |
| Auto-Mobile (Grantham) Ltd | Wholesale & retail | 2012 |
| Autocraft Drivetrain Solutions Limited | Manufacturing | 1993 |
| Autocraft EV Solutions Limited | Manufacturing | 2018 |
| Autocraft Machining Solutions Ltd | Manufacturing | 2018 |
| Autocraft Solutions Group Limited | Manufacturing | 2018 |
| Autocraft Solutions Limited | Manufacturing | 2018 |