| Atrum Global Limited | London | 2017 |
| Atrytone Group Ltd | Camberley | 2026 |
| ATS Capital Limited | Brentwood | 2023 |
| ATS Finance Ltd | Market Harborough | 2025 |
| ATS Financial Services and Consultancy Limited | Manchester | 2025 |
| ATS Group Holdings Ltd | Tadley | 2023 |
| ATS Group Members Ltd | Maidstone | 2019 |
| ATS Investment Holdings Limited | London | 2023 |
| ATS Media Group Limited | Havant | 2022 |
| ATS Real Estate Holdings Limited | London | 2022 |
| ATS Sharing Ltd | London | 2020 |
| Atsfinancialservices Ltd | Cramlington | 2023 |
| Atsika Ltd | London | 2023 |
| Atspeed Group Ltd | Brighton | 2016 |
| ATT Property Ltd | Folkestone | 2021 |
| Atta Holdings Limited | Ilkeston | 2015 |
| Attache Limited | Altrincham | 2000 |
| Attachment Group Limited | London | 2019 |
| Attain Financial Solutions Limited | Wellingborough | 2018 |
| Attain Holdings Limited | Derby | 2026 |
| Attain Investments Limited | Derby | 2026 |
| Attakon Limited | Birmingham | 2025 |
| Attalus Investments Ltd | Camberley | 2019 |
| Attanayake Trading Ltd | West Drayton | 2025 |
| Attanta Limited | Manchester | 1995 |
| Attapoll Holdings Ltd | Beaconsfield | 2021 |
| Attara Limited | London | 2022 |
| Attarewards Holdings Ltd | Beaconsfield | 2026 |
| Attechy Ltd | London | 2025 |
| Atten Bidco Limited | Derby | 2021 |
| Atten Finance Limited | Derby | 2021 |
| Atten Group Limited | Derby | 2021 |
| Atten Midco Limited | Derby | 2021 |
| Attenborough Financial Planning Ltd | Tunbridge Wells | 2024 |
| Attenborough Industrial Doors Limited | Nottingham | 1997 |
| Attentif Ltd | London | 2022 |
| Attention Industries Limited | Bristol | 2018 |
| Attento Management Holdings Limited | Liphook | 2020 |
| Attento Underwriting Agency Limited | London | 2020 |
| Attentus Financial Planning Ltd | Exeter | 2024 |
| Atters Investments Limited | Guildford | 2026 |
| Atterton and Ellis Holdings Limited | Rugby | 2023 |
| Attestor Investments Limited | London | 2026 |
| Attestor Limited | London | 2019 |
| Attestor Services Limited | London | 2011 |
| Attfield James Limited | Axminster | 1993 |
| Atthegroup Limited | London | 2026 |
| Attheraces Holdings Limited | London | 2001 |
| Atti International Limited | Reading | 2004 |
| Attic Group Ltd | Poole | 2025 |
| Attic Holdco Limited | Oldbury | 2025 |
| Attic Holdings Limited | Leicester | 2021 |
| Attic Propco Limited | Oldbury | 2025 |
| Attica Capital Ltd | Leigh-On-Sea | 2014 |
| Attica Holdings Limited | Weybridge | 2020 |
| Atticus Financial Planning Ltd | Alton | 2020 |
| Atticus Investment Holdings Ltd | Reigate | 2023 |
| Atticus Risk Solutions Limited | Stourbridge | 2021 |
| Attijariwafa Limited | London | 2002 |
| Attik Invest Limited | London | 2022 |
| Attilus Enterprises Ltd. | London | 2014 |
| Attinger Jack Holdings Limited | Bath | 2011 |
| Attis Holdings Unlimited | London | 2017 |
| Attis Insurance Brokers Ltd | Leeds | 2020 |
| Attis Northern Limited | Leeds | 2021 |
| Attivo Buckingham Gate Limited | Cheltenham | 2025 |
| Attivo Corporate Planning Limited | Cheltenham | 2021 |
| Attivo Financial Planning Limited | Cheltenham | 2006 |
| Attivo Financial Services Limited | Cheltenham | 2006 |
| Attivo Investments Holdings Limited | Cheltenham | 2024 |
| Attivo Investments Limited | Cheltenham | 2024 |
| Attivo Ltd | London | 2021 |
| Attivo Mortgage and Protection Limited | Cheltenham | 2021 |
| Attivo Partner Limited | Cheltenham | 2025 |
| Attivo Private Clients Limited | Cheltenham | 2021 |
| Attivo Private Office Limited | Cheltenham | 2024 |
| Attlas Commercial Finance Limited | Birmingham | 2026 |
| Attosh Holdings Limited | Hatfield | 2025 |
| Attraction World Group Limited | Birmingham | 2020 |
| Attraction World Holdings Limited | Birmingham | 2010 |
| Attraction World Ventures Limited | Birmingham | 2020 |
| Attrell Group Limited | Bexhill | 2026 |
| Attritium Ltd | London | 2021 |
| Attwater Group Limited | Preston | 2025 |
| Attwell Family Investment Company Limited | Redditch | 2021 |
| Attwell Holdings Ltd | Bristol | 2024 |
| Attwood Land Ltd | Cheltenham | 2024 |
| Attwoods Limited | Maidenhead | 1939 |
| Atty Group Ltd | Maidenhead | 2025 |
| ATU Investments Ltd. | South Shields | 2022 |
| Atubem Ltd | London | 2025 |
| Atuk Group Ltd | Liverpool | 2025 |
| Atunara Group Ltd | Bristol | 2025 |
| ATV Global Limited | Witney | 2020 |
| ATV Holdings Ltd | London | 2021 |
| ATW Collective Ltd | Cardiff | 2025 |
| ATW Financial Services Ltd | Sheffield | 2020 |
| ATW Holdings Limited | Reading | 2015 |
| Atwal (BI) Holdings Limited | Coventry | 2021 |
| Atwal Group Limited | Wednesbury | 2016 |