| 3 AM Group Limited | Knebworth | 2021 |
| 3 and a Half Ltd | Newcastle Upon Tyne | 2025 |
| 3 and Five Technology Limited | Ilford | 2013 |
| 3 Barra Ltd | Eastleigh | 2007 |
| 3 Barrels Media Limited | Mitcham | 2012 |
| 3 Beans Consulting Ltd | Luton | 2024 |
| 3 Beat Music Ltd | Liverpool | 2014 |
| 3 Beat Productions Limited | Liverpool | 2007 |
| 3 Birds Limited | Looe | 2007 |
| 3 Bravo Limited | Aberdeen | 2025 |
| 3 Bravo Tech Limited | Aberdeen | 2025 |
| 3 Cats Group Limited | London | 2019 |
| 3 Chillies Consulting Ltd | Slough | 2015 |
| 3 Chillies Limited | Reading | 1999 |
| 3 Circle Limited | Cheltenham | 2009 |
| 3 Circles Communications Limited | Basingstoke | 2013 |
| 3 Clicks Right Ltd | Caterham | 2021 |
| 3 Cliffs Bay Productions Limited | London | 2025 |
| 3 Core AV Ltd | Caerphilly | 2018 |
| 3 Counties Consultants Limited | Crawley | 2004 |
| 3 D Interiors Limited | Bristol | 1996 |
| 3 Dads Walking Limited | Penrith | 2021 |
| 3 Degrees Media Limited | Leicester | 2013 |
| 3 Dish Digital Solutions Ltd | London | 2026 |
| 3 Donkeys Ltd | Okehampton | 2017 |
| 3 Doors Limited | London | 2021 |
| 3 EYE Infopark Limited | Bristol | 2016 |
| 3 Eyes Global Limited | London | 2022 |
| 3 Feet High Limited | Crowborough | 2005 |
| 3 Films Limited | Hackney | 2014 |
| 3 Finch Ltd | Dundee | 2019 |
| 3 for Luck Limited | Lymington | 2025 |
| 3 G Telecommunications Limited | Leeds | 2005 |
| 3 Ginger Ltd | Rickmansworth | 2015 |
| 3 H T S Limited | Sheffield | 2014 |
| 3 High Street Wrexham Ltd | Wrexham | 2025 |
| 3 Horizons Capital Ltd | Abingdon | 2010 |
| 3 Hurdles Ltd | London | 2023 |
| 3 Kaurs Consulting Limited | Cheltenham | 2025 |
| 3 Kaurs Infotech Limited | Cheltenham | 2025 |
| 3 Kingdoms Group Ltd | Wimborne | 2021 |
| 3 Kingpins Limited | Bromsgrove | 2020 |
| 3 Laws Entertainment Ltd. | Harrow | 2023 |
| 3 Legged Bear Productions Limited | Bromley | 2009 |
| 3 Line Design Ltd | Macclesfield | 2023 |
| 3 Lives Movie Limited | Bridgwater | 2016 |
| 3 Loop Music Limited | London | 2011 |
| 3 MAD MEN Ltd | Wrexham | 2024 |
| 3 Million Words Ltd | London | 2026 |
| 3 Minute Records Limited | Sutton | 2008 |
| 3 Minutes West Ltd | Manchester | 2016 |
| 3 Missed Calls Ltd | London | 2025 |
| 3 Oaks Studios Ltd | Coleraine | 2025 |
| 3 of Life Limited | Bushey | 2026 |
| 3 on Ltd | Birmingham | 2019 |
| 3 Owls Consulting Ltd | London | 2025 |
| 3 Phase Control Ltd | Kent | 2009 |
| 3 PHE Limited | Epsom | 2010 |
| 3 Point Consulting Limited | Towcester | 2024 |
| 3 Point Media Limited | Darlington | 2014 |
| 3 Powell Productions Limited | Crowborough | 2008 |
| 3 Quotes Limited | West Yorkshire | 2000 |
| 3 REX Limited | Lydney | 2016 |
| 3 Rose Media Ltd | Nairn | 2015 |
| 3 Seed Solutions Ltd | Worcester | 2012 |
| 3 Sheep Limited | London | 2008 |
| 3 Shilling Dream Music, Arts & Publishing Ltd | Isle Of Cumbrae | 2024 |
| 3 Sided Cube (UK) Ltd | Salisbury | 2005 |
| 3 Sided Cube (USA) Ltd | Salisbury | 2020 |
| 3 Sixty Studios Limited | London | 2004 |
| 3 Spirits Productions Limited | London | 2025 |
| 3 SPY Limited | Lynch Wood, Peterborough | 2002 |
| 3 Suns Broadcast Solutions Limited | Loughborough | 2009 |
| 3 Technology Limited | Leeds | 2013 |
| 3 Tier Systems UK Limited | Newcastle Upon Tyne | 2001 |
| 3 Trees Consulting Ltd | Glasgow | 2010 |
| 3 V Media Limited | Derby | 2015 |
| 3 Vine Street Limited | Melton Mowbray | 2010 |
| 3 Wheelers Limited | London | 2005 |
| 3 Widows Limited | London | 2022 |
| 3 Wishes for Christmas Limited | Bristol | 2023 |
| 3 X CMS Ltd | Dudley | 2015 |
| 3 X League Ltd | London | 2020 |
| 3'S a Crowd Studios Ltd. | Oxford | 2021 |
| 3-2-1 Launch Ltd | London | 2023 |
| 3-2-1-GOCHECK Limited | Wembley | 2021 |
| 3-56 Media Limited | West Linton | 2011 |
| 3-D CAD Creations Limited | Northampton | 2007 |
| 3-FOLD Games Ltd | London | 2019 |
| 3-WAVES Media Project CIC | London | 2025 |
| 3.14 Pictures Ltd | London | 2024 |
| 3.14ZDEC Ltd | London | 2024 |
| 3.25 Digital Consultancy Limited | Stockport | 2016 |
| 30 Characters Limited | South Woodham Ferrers | 2021 |
| 30 Decades Ltd | London | 2022 |
| 30 Moon Limited | Glasgow | 2022 |
| 30 October Ltd | Hemel Hempstead | 2009 |
| 30 Year Publication Ltd. | Feltham | 2017 |
| 30.06 Studios Ltd | Sunderland | 2010 |
| 300 Consulting Limited | Swindon | 2008 |