| Alternative Development Finance Limited | Borehamwood | 2021 |
| Alternative Distribution Partners Ltd | London | 2024 |
| Alternative Energy Company Limited | London | 2025 |
| Alternative Estates & Financial Services Limited | | 1990 |
| Alternative Finance Group Ltd | Pudsey | 2019 |
| Alternative Financial Solutions Limited | Orpington | 2011 |
| Alternative Flooring Holdings Limited | Andover | 2019 |
| Alternative Funding Centre Limited | Leamington Spa | 2015 |
| Alternative Income Reit PLC | London | 2017 |
| Alternative Investment Solutions (Management) Limited | Croydon | 2009 |
| Alternative Mason Investments Limited | Tenbury Wells | 2021 |
| Alternative Payments Limited | London | 2012 |
| Alternative Primeur Group Ltd. | Northwich | 2014 |
| Alternative Propositions Limited | Stockport | 2012 |
| Alternative Pubs Group Limited | Southampton | 2021 |
| Alternative Strategies Limited | Hemel Hempstead | 2018 |
| Alternative Windows (Leeds) Holdings Limited | Leeds | 2019 |
| Alternatives Advisory Ltd | West Byfleet | 2025 |
| Alterno Wealth Limited | Leicester | 2015 |
| Altero Capital Holdings Limited | London | 2021 |
| Altero Capital UK Ltd | London | 2019 |
| Alterra at Lloyd's Limited | London | 1997 |
| Alterra Corporate Capital 3 Limited | London | 2002 |
| Alterum Consultancy Ltd | Renfrew | 2016 |
| Alterum Limited | Wellingborough | 2011 |
| Alterx Holdings Limited | London | 2021 |
| Alterx Living Limited | London | 2022 |
| Alterxchange Limited | London | 2025 |
| Altery Ltd | London | 2009 |
| Altex Holdings Bradford Limited | Leeds | 2010 |
| Altex Industrial Holdings Limited | Rochford | 2013 |
| Altgolan Wind Farm Holdings Limited | Belfast | 2022 |
| Altham Holdings Limited | London | 2022 |
| Altham International Limited | Accrington | 1998 |
| Althams Food Group Limited | Morecambe | 2019 |
| Althara Holdings Limited | London | 2025 |
| Althea Wellness Limited | London | 2025 |
| Althemis Capital Ltd | London | 2026 |
| Althera Group Ltd | Alresford | 2026 |
| ALTHERA42 Capital Partners Limited | London | 2026 |
| Althing Limited | London | 2025 |
| Althoff & Associates Ltd | Middlesex | 2007 |
| Alti Alternative Holdings Limited | London | 2025 |
| Alti Alternative Investment Management Limited | London | 2025 |
| Alti Asset Management Holdings 2 Limited | Birmingham | 2014 |
| Alti Asset Management Holdings Limited | Birmingham | 2021 |
| Alti Global Wealth Management Holdings Limited | London | 2021 |
| Alti Holdings Ltd | Antrim | 2026 |
| Alti International Operations Limited | London | 2018 |
| Alti Pradera Holdings Limited | Birmingham | 2016 |
| Alti RE Limited | Birmingham | 2009 |
| Alti RE Public Markets Limited | Birmingham | 2022 |
| Alti Strategic Advisory (UK) Limited | Birmingham | 2018 |
| Alti Wealth Management (UK) Limited | London | 2010 |
| Alti Wealth Management Holdings (UK) 2 Limited | London | 2010 |
| Alti Wealth Management Holdings (UK) Limited | London | 2021 |
| Altify UK Limited | London | 2025 |
| Altilde Ltd | Liverpool | 2021 |
| Altilium Group Limited | London | 2018 |
| Altilium Licensing Limited | London | 2018 |
| Altim Software Limited | Cirencester | 1998 |
| Altimapa Capital Limited | London | 2015 |
| Altimapa Limited | London | 2016 |
| Altimist Capital Ltd | London | 2024 |
| Altimus Holding Co Limited | Manchester | 2026 |
| Altincik Holdings Limited | London | 2025 |
| Altinel & Co Limited | London | 2019 |
| Altini Holdings Limited | Crowthorne | 2026 |
| Altinini Investments Ltd | London | 2019 |
| Altinvst Ltd | Kirkcaldy | 2026 |
| Altior Holdings Limited | Durham | 2018 |
| Altiora Capital Limited | Leeds | 2025 |
| Altiora Group Ltd | Bracknell | 2022 |
| Altip Holdings Limited | Quorn | 2022 |
| Altir Underwriting Limited | London | 1999 |
| Altis Holdings Limited | Solihull | 2026 |
| Altis Partners Limited | London | 2022 |
| Altitude 1850 Ltd | Manchester | 2022 |
| Altitude Aviation Group Ltd | Ford End | 2022 |
| Altitude Aviation Limited | Chelmsford | 2008 |
| Altitude Bidco Limited | Worcestershire | 2025 |
| Altitude Capital Management Limited | London | 2020 |
| Altitude Capital Services Ltd | London | 2022 |
| Altitude Financial Solutions Limited | Nottingham | 2025 |
| Altitude Funding Solutions Ltd | Castlefield | 2019 |
| Altitude Holdco Limited | Altrincham | 2026 |
| Altitude Insurance Brokers Ltd | Worthing | 2023 |
| Altitude Investment Management PLC | London | 2019 |
| Altitude Midco Limited | Worcestershire | 2025 |
| Altitude Mortgages Ltd | Epping | 2022 |
| Altitude Topco Limited | Worcestershire | 2025 |
| Altium Investment Management Limited | Banbury | 2018 |
| Altius Bavaria Limited | London | 2025 |
| Altius Business Services Limited | Goole | 2026 |
| Altius Capital Ltd | Cheltenham | 2012 |
| Altius Corporate Design and Build Limited | Christchurch | 2001 |
| Altius Group Holdings Limited | Preston | 2025 |
| Altius Huguenot Limited | London | 2025 |
| Altius IFA Limited | York | 2025 |
| Altius Two IFA Limited | York | 2026 |