| AT9 Wholesale Ltd | Wholesale & retail | 2025 |
| ATA Construction Services Ltd | Construction | 2022 |
| ATB Trading Ltd | Wholesale & retail | 2023 |
| ATC Repair Centre Limited | Wholesale & retail | 2023 |
| ATC Transport 1 Limited | Transport & logistics | 2019 |
| ATC Treadmaster Ltd | Wholesale & retail | 2026 |
| Atco Investments Limited | Financial services | 2024 |
| ATD Hospitality Ltd | Hospitality | 2023 |
| ATF Cleantec Limited | Administrative & support | 2024 |
| Athena APD Ltd | Construction | 2020 |
| Athiaa Ltd | Health & social care | 2022 |
| Athletech Ltd | Wholesale & retail | 2024 |
| ATI Tyre Recycling Ltd | Wholesale & retail | 2019 |
| Atjw Property Limited | Real estate | 2016 |
| Atkin Brothers Ltd | Wholesale & retail | 2024 |
| Atkinson & Company Intellectual Property Limited | Professional & scientific | 1999 |
| Atkinson Wheller Limited | Professional & scientific | 2005 |
| ATL Brickwork Ltd | Construction | 2014 |
| Atlantic Court (Woolacombe) Management Company Limited | Households | 1997 |
| Atlas Court Management Company Ltd | Real estate | 2012 |
| Atlas Industrial Park Limited | Education | 2020 |
| Atlas Training Solutions Ltd | Education | 2022 |
| ATM Rapid Repair Ltd | Wholesale & retail | 2011 |
| Atnas Boxing Media Ltd | Information & communication | 2026 |
| Atom Architectural Limited | Professional & scientific | 2024 |
| Atoms Joinery Limited | Construction | 2023 |
| Atqcare Limited | Health & social care | 2025 |
| Atr-Bdm Consulting Ltd | Construction | 2018 |
| Atrium Self Storage Ltd | Transport & logistics | 2019 |
| Atropa Limited | Extraterritorial | 2016 |
| ATS Engineering Ltd | Manufacturing | 2017 |
| ATS Grabs & Attachments Ltd | Wholesale & retail | 2024 |
| Atsaal Limited | Wholesale & retail | 2022 |
| Attain Skills & Knowledge Ltd | Administrative & support | 2010 |
| Attentional Machines Limited | Manufacturing | 2010 |
| Attercliffe Assets Limited | Administrative & support | 2009 |
| Atthebuzzeruk Ltd | Wholesale & retail | 2024 |
| Atuin.Events Ltd | Hospitality | 2023 |
| AUC Professional Services Ltd | Professional & scientific | 2019 |
| Auckland Property Holdings Limited | Real estate | 2021 |
| Audais Ltd | Wholesale & retail | 2026 |
| Audax Sound System Limited | Extraterritorial | 1964 |
| Auditoria Services Limited | Manufacturing | 1977 |
| Augmented Management Solutions Limited | Other services | 2015 |
| August Music Limited | Information & communication | 2012 |
| Aura & Earth Ltd | Construction | 2026 |
| Aura Land Ltd | Real estate | 2022 |
| Aura Medical Services Ltd | Health & social care | 2025 |
| Aura Pilates & Wellness Studio Ltd | Arts & recreation | 2025 |
| Aura Property (Yorks) Ltd | Real estate | 2021 |
| Auro Master Ltd | Wholesale & retail | 2015 |
| Aurum House Limited | Mining & quarrying | 2015 |
| Aurum Property Developments Ltd | Construction | 2023 |
| Auto D Ltd | Wholesale & retail | 2022 |
| Auto Electrics Rotherham Ltd | Wholesale & retail | 2018 |
| Auto Hub Tyres MOT & Repaire Ltd | Wholesale & retail | 2026 |
| Auto P Fect Limited | Wholesale & retail | 2010 |
| Auto Trade Corporation Ltd | Wholesale & retail | 2022 |
| Auto-Mobile Smart Repair Limited | Wholesale & retail | 2014 |
| Autoclave Hire Limited | Other services | 2017 |
| Autoclave Repairs Ltd | Professional & scientific | 2021 |
| Autocraft (Rotherham) Ltd | Wholesale & retail | 2013 |
| Autocraft Motor Caravans Limited | Wholesale & retail | 1999 |
| Autoit Ltd | Information & communication | 2025 |
| Automation REM Ltd | Manufacturing | 2015 |
| Automobile Repair Services Ltd | Wholesale & retail | 2021 |
| Automotive Car Sales Ltd | Wholesale & retail | 2025 |
| Automotive Link Ltd | Professional & scientific | 2026 |
| Autoparts Republic Ltd | Wholesale & retail | 2026 |
| Autoplanus Limited | Wholesale & retail | 2006 |
| Autraguard Ltd | Administrative & support | 2025 |
| AVA Property and Holdings Ltd | Real estate | 2023 |
| Avalon ER Ltd | Financial services | 2025 |
| Avant Moto Design Ltd | Wholesale & retail | 2019 |
| Aven Tools Limited | Professional & scientific | 1970 |
| Avenzaco Capital Limited | Administrative & support | 2013 |
| Averie Property Holdings Limited | Real estate | 2021 |
| Avibel Ltd | Wholesale & retail | 2026 |
| Aviclean Solutions Ltd | Administrative & support | 2025 |
| AVS Technik Ltd | Wholesale & retail | 2013 |
| Avs-Comm Limited | Administrative & support | 2006 |
| AVT Reliability Ltd | Professional & scientific | 1984 |
| Avtpump Limited | Manufacturing | 1997 |
| AW Aluminium Limited | Manufacturing | 2007 |
| AW Plastering Nationwide Ltd | Construction | 2025 |
| Awandirect Ltd | Wholesale & retail | 2026 |
| Awas AA Limited | Real estate | 2024 |
| Awatts Ltd | Hospitality | 2026 |
| AWC Roofing Ltd | Construction | 2020 |
| AWD Software Limited | Professional & scientific | 2012 |
| AWS275 Ltd | Hospitality | 2024 |
| Axel Brothers Customs Limited | Wholesale & retail | 2025 |
| Axiom Project Solutions Ltd | Professional & scientific | 2025 |
| Axon Modern Ltd | Manufacturing | 2020 |
| Axonpol Ltd | Wholesale & retail | 2026 |
| Axxilia Group Ltd | Information & communication | 2023 |
| Ayaaz Limited | Financial services | 2017 |
| Ayan Market S62 Limited | Wholesale & retail | 2024 |
| Ayaz Burger Ltd | Hospitality | 2026 |
| Ayesentialpicks Ltd | Wholesale & retail | 2025 |