| Aspect Electronics Limited | Professional & scientific | 2004 |
| Aspect Trustees Limited | Administrative & support | 2022 |
| Aspects International Limited | Professional & scientific | 1990 |
| Aspirational Education Limited | Education | 2011 |
| Aspirational Learning Limited | Education | 2011 |
| Aspire (Yorkshire) LLP | | 2011 |
| Aspire Cleaning Solutions Ltd | Administrative & support | 2025 |
| Aspire Properties Holdings Limited | Real estate | 2016 |
| Aspirebc Ltd | Professional & scientific | 2023 |
| Aspiring Nations Limited | Administrative & support | 2021 |
| Asquith Limited | Extraterritorial | 2026 |
| Asro Limited | Professional & scientific | 2022 |
| Assemble Publicity Limited | Professional & scientific | 2020 |
| Assess on Demand Limited | Information & communication | 2023 |
| Asset Hound Limited | Information & communication | 2026 |
| Asset Release Management Newco Limited | Real estate | 2023 |
| Association of Independent Meat Suppliers | Other services | 2002 |
| Assured Asset Management Consulting Limited | Construction | 2015 |
| Assured Financial Planning Limited | Financial services | 2016 |
| Assured Property Acquisitions Limited | Real estate | 2009 |
| Astar Research Ltd | Financial services | 2026 |
| Astley International Limited | Extraterritorial | 2025 |
| Aston Brooks Limited | Extraterritorial | 2025 |
| Aston Fuller Limited | Extraterritorial | 2021 |
| Aston Goodwin Limited | Extraterritorial | 2025 |
| Astor Ltd | Real estate | 2013 |
| Astrid Holdings Limited | Financial services | 2025 |
| Astrum Planning Ltd | Professional & scientific | 2020 |
| Astute Health Ltd | Health & social care | 2017 |
| ATA Consultants Limited | Professional & scientific | 2007 |
| ATC Business Recovery Services Limited | Professional & scientific | 2014 |
| Atelier B Projects Limited | Professional & scientific | 2026 |
| Athena Consulting Ltd | Professional & scientific | 2024 |
| Athlete Life Limited | Information & communication | 2024 |
| Athlete Transition Accelerator Ltd | Education | 2022 |
| Atis Living Limited | Real estate | 2020 |
| Atkinson and Clarke Limited | Real estate | 2024 |
| Atkinson Garden Services Limited | Other services | 2025 |
| Atkinson LET Properties Ltd | Real estate | 2020 |
| ATL Contractors Limited | Construction | 2012 |
| Atlantas Group Ltd | Public administration | 2019 |
| Atlas Helicopters Limited | Transport & logistics | 2001 |
| Atomic Dealer Ltd | Information & communication | 2020 |
| Atomstream Telecom Ltd | Information & communication | 2024 |
| ATS Interiors Ltd | Construction | 2023 |
| Atta Forever Limited | Manufacturing | 2020 |
| Attained UK Ltd | Real estate | 2022 |
| Aubrey Green French Polisher Ltd | Wholesale & retail | 2016 |
| Auclair Limited | Wholesale & retail | 2022 |
| Audience Marketing Limited | Professional & scientific | 2021 |
| Audient Consulting Ltd | Information & communication | 2016 |
| Audio Archtct Experience Ltd | Hospitality | 2022 |
| Audio Burn Ltd | Information & communication | 2008 |
| Audio Events Limited | Administrative & support | 2003 |
| Audiyocloud Limited | Wholesale & retail | 2025 |
| Audley Court Estates Limited | Health & social care | 1997 |
| Audley Court Hollins Hall Limited | Real estate | 2001 |
| Aurelie Group Ltd | Wholesale & retail | 2020 |
| Aurora Search Consultants Ltd | Administrative & support | 2018 |
| Aurora Testing Services Limited | Other services | 2017 |
| Austin Rand Limited | Extraterritorial | 2011 |
| Authentic Intelligence Limited | Professional & scientific | 2024 |
| Authentic Wholesale Services Limited | Wholesale & retail | 2020 |
| Autism Angels Ltd | Health & social care | 2012 |
| Auto-Logic Harrogate Limited | Wholesale & retail | 2021 |
| Autobody Accident Repair Centres Limited | Wholesale & retail | 2024 |
| Autoelectron Limited | Professional & scientific | 2014 |
| Autoimmune Nutrition Clinic Ltd | Health & social care | 2019 |
| Automation 4 Ltd | Manufacturing | 2004 |
| Automotive Finance & Leasing Ltd | Administrative & support | 2005 |
| Autospire Specialist Cars Ltd | Wholesale & retail | 2021 |
| Autumnwood Media Limited | Information & communication | 2014 |
| AV8H Limited | Education | 2021 |
| AVA Alms Valve Agency Ltd | Wholesale & retail | 2009 |
| Avalanche Direct Limited | Information & communication | 2002 |
| Avalon Group (Social Care) | Health & social care | 1994 |
| Avec Coffee Limited | Manufacturing | 2019 |
| Avenir (Wakefield) Limited | Professional & scientific | 2007 |
| Aventel Limited | Manufacturing | 2012 |
| Avenue 445 Ltd | Real estate | 2025 |
| Averre Group Limited | Financial services | 2009 |
| Avery Rose Properties Ltd | Real estate | 2025 |
| Aviator Court Management Limited | Households | 1998 |
| Aviator Developments Limited | Real estate | 2016 |
| AVL Projects (North) Ltd | Construction | 2026 |
| AVM Create Ltd | Arts & recreation | 2021 |
| Avon GAS and Plumbing Ltd | Construction | 2024 |
| Avrox Technologies Ltd | Professional & scientific | 2014 |
| AW Homes Limited | Real estate | 2008 |
| Award Air Ltd | Professional & scientific | 2015 |
| Award Energy Consultants 2 Limited | Financial services | 2024 |
| Award Energy Consultants Limited | Administrative & support | 2005 |
| Awesome-Intelligence Ltd | Information & communication | 2019 |
| Awsome Ltd | Extraterritorial | 2012 |
| AXE Racing Ltd | Arts & recreation | 2019 |
| Axebell Limited | Real estate | 2012 |
| Axiom Accounting 39 Limited | Professional & scientific | 2016 |
| Axiom Construction Harrogate Limited | Construction | 2016 |
| Axiom Partnering Solutions Ltd | Professional & scientific | 2020 |
| AXM (Beverley Place) Limited | Construction | 2023 |