| Adcelerate Ltd | London | 2025 |
| Adcentra Limited | Ilford | 2025 |
| Adcentric Ltd | Rochester | 2020 |
| Adcept Consulting Limited | Wisbech | 2014 |
| Adcept Ltd | Windsor | 2023 |
| Adchievable Limited | Bournemouth | 2016 |
| Adcity UK Limited | Maidstone | 2015 |
| Adclaas Media Limited | Harrow | 2026 |
| Adclaro Limited | London | 2013 |
| Adclinic Ltd | Worthing | 2025 |
| Adclipup Ltd | London | 2025 |
| Adclix Ltd | London | 2023 |
| Adcms Ltd | Cheltenham | 2004 |
| Adco Consult Ltd | London | 2025 |
| Adco Contracting Limited | Nottingham | 2016 |
| Adco Engineering Limited | Nottingham | 2009 |
| Adco Legal Limited | Bury | 2021 |
| Adco Media Ltd | Leicester | 2024 |
| Adco Rail Limited | Altrincham | 2021 |
| Adcock Analysis Ltd | London | 2016 |
| Adcock Consulting Limited | Hardwick | 2010 |
| Adcocks (Holdings) Limited | Lichfield | 2024 |
| Adcocks Solicitors Limited | Staffordshire | 2001 |
| Adcohealth Consultancy Limited | Poole | 2015 |
| Adcolony UK Limited | London | 2006 |
| Adcombe Consulting Limited | Taunton | 2022 |
| Adcompany Ltd | Robertsbridge | 2012 |
| Adcon Consultancy Ltd | Wirral | 2018 |
| Adcon Holdings Limited | Birmingham | 1961 |
| Adcotx Therapeutics Ltd | London | 2026 |
| Adcox Limited | Eastbourne | 2010 |
| Adcrafters Ltd | London | 2026 |
| Adcrate Ltd | Slough | 2022 |
| Adcredible Ltd | Morecambe | 2010 |
| Adcroft Holding Inc. Limited | Chester | 2007 |
| Adcult Ltd | Harrow | 2026 |
| Adcuratus Limited | London | 2023 |
| Adcuris Consulting Limited | Shrewsbury | 2017 |
| ADD 4 U Ltd | Watford | 2020 |
| ADD Accountancy Limited | Aberdeen | 2003 |
| ADD Accounting Solutions Limited | Peebles | 2017 |
| ADD Agency Limited | Usk | 2006 |
| ADD Agency London Ltd | Plymouth | 2021 |
| ADD AM Design Limited | Bedworth | 2014 |
| ADD and Subtract Limited | London | 2023 |
| ADD APT Architects Ltd | London | 2023 |
| ADD Architecture Limited | Paisley | 2024 |
| ADD Balance Limited | Reigate | 2020 |
| ADD Bookkeeping Ltd | Nottingham | 2015 |
| ADD Capital Limited | Ashford | 2022 |
| ADD Consultancy Ltd | King'S Lynn | 2010 |
| ADD Consulting and Advisory Limited | London | 2024 |
| ADD Consulting Engineers Ltd | Craigavon | 2023 |
| ADD Contracts (Civils) Ltd | Stirling | 2023 |
| ADD Digital Ltd | Witham | 2025 |
| ADD Energy Scotland Limited | Aberdeen | 2010 |
| ADD Engineering Solutions Ltd | Leighton Buzzard | 2026 |
| ADD Food Network Ltd | Nr Church Stretton | 2018 |
| ADD Graphene Group Limited | Basingstoke | 2024 |
| ADD Healthcare Management Limited | Leyland | 2013 |
| ADD Impact Advisory Ltd | Carterton | 2025 |
| ADD Item to Ltd | Dudley | 2025 |
| ADD Leife Limited | London | 2021 |
| ADD Lemonade Limited | Bournemouth | 2020 |
| ADD LIV Ltd | Gloucester | 2019 |
| ADD London Consultancy Limited | London | 2020 |
| ADD Management Ltd | London | 2009 |
| ADD Marketing Ltd | Dudley | 2021 |
| ADD Media Ltd | London | 2026 |
| ADD Melon Ltd | Crowthorne | 2020 |
| ADD Mgmt Ltd | Brierley Hill | 2023 |
| ADD More Value Communication Ltd | Morecambe | 2007 |
| ADD One (Scotland) Limited | Irvine | 2000 |
| ADD One Business Services Limited | West Calder | 2003 |
| ADD Safety Limited | Wynyard | 2021 |
| ADD Skills Limited | Stafford | 2018 |
| ADD Strategy Ltd | Newcastle Upon Tyne | 2015 |
| ADD Then Multiply Limited | London | 2010 |
| ADD This Limited | Gloucestershire | 2003 |
| ADD to (Taste), Design and Advertising Limited | Harpole | 1999 |
| ADD US on Limited | Falkirk | 2022 |
| ADD Value Accountancy Limited | Kent | 2007 |
| ADD Value Home Ltd | London | 2021 |
| ADD- Worth Accountancy Ltd | Banbury | 2020 |
| Add-It-Up Ltd | Egham | 2020 |
| Add-Itions Accountancy Solutions Limited | Nottingham | 2008 |
| Add-Tech Testing Services Limited | Ashford | 2026 |
| Add-Vance Solutions Limited | Hove | 2010 |
| Add-Vanced Bookkeeping Services Ltd | Todmorden | 2009 |
| Add.Law Limited | London | 2017 |
| Add/Projects Limited | Milton Keynes | 2019 |
| ADD10 Limited | London | 2017 |
| Adda PLC | London | 2025 |
| Adda Sendero Limited | London | 2026 |
| Addacas Accounting Limited | Rushden | 2019 |
| Addae Ltd | London | 2023 |
| Addaesie Ltd | Newbury | 2025 |
| Addapta Solutions Limited | Borehamwood | 2009 |
| Addaptive Group Limited | Hitchin | 2020 |
| Addato Limited | Kenilworth | 2011 |