| C.N. Air-Mach Limited | Manchester | 1985 |
| C.N. Controls Limited | Banbury | 1998 |
| C.N. Ross-Field Manufacturing Jewellers Limited | | 1978 |
| C.N.C. Manufacturing Limited | Matlock | 1997 |
| C.N.C. Punching Limited | Leicester | 1980 |
| C.Nicol Ltd | Grantown-On-Spey | 2013 |
| C.O'Donovan & Sons Limited | Leeds | 2018 |
| C.O. Plant Services Limited | Leeds | 2018 |
| C.Olley & Sons,Limited | Bury St. Edmunds | 1917 |
| C.P. (Arts) Limited | Exeter | 1976 |
| C.P. Metalwork Solutions Limited | Leighton Buzzard | 2012 |
| C.P. Steelworks Limited | Chichester | 2002 |
| C.P. Wisher Limited | Maidstone | 2013 |
| C.P. Witter Limited | Shrewsbury | 1978 |
| C.P.A. Engineering Limited | Kent | 1980 |
| C.P.A. Fabrications Limited | Birmingham | 1993 |
| C.P.D.S. Machinery Limited | Oldham | 2002 |
| C.P.G Plastech Limited | Bradford | 2017 |
| C.P.L Precision Engineering Limited | Wetherby | 2004 |
| C.P.S Trailers Ltd | Bromborough | 2024 |
| C.P.S. (Wales) Limited | Caerphilly | 1995 |
| C.Perkins Joinery Limited | Dover | 2023 |
| C.R Brown Nottingham Limited | Nottingham | 2004 |
| C.R. Clarke & Co. (UK) Limited | Ammanford | 1986 |
| C.R. Utting Limited | North Walsham | 1998 |
| C.R. Willcocks and Company Limited | Droitwich Spa | 1984 |
| C.R. Windows (Avon) Limited | Kingswood | 1978 |
| C.R.Blade Services Ltd | Middlesbrough | 2018 |
| C.R.D. Devices Ltd. | Shildon | 1995 |
| C.R.D. Engineering Solutions Ltd | Dukinfield | 2024 |
| C.R.D.S. Limited | Leamington Spa | 2004 |
| C.R.E.M.E. (Industrial Solutions) Ltd | Nottingham | 2013 |
| C.R.Engineering Works(Waddesdon)Limited | St. Albans | 1970 |
| C.R.S Marine Carpentry Ltd | Cambridge | 2024 |
| C.Rown & Empire Camping Company Ltd | Bridport | 2019 |
| C.Rushton UK Ltd | Wirral | 2025 |
| C.S Avionic Solutions Ltd | Stockport | 2025 |
| C.S. Engineering (NW) Limited | Rossendale | 2019 |
| C.S. Engineering (South East) Limited | St. Leonards-On-Sea | 2016 |
| C.S. Fabs Limited | Leeds | 2008 |
| C.S. Morphet and Sons Limited | Liverpool | 1986 |
| C.S. Podd & SON Limited | Whyteleafe | 1981 |
| C.S. Properties (Northern) Limited | Haydock | 1969 |
| C.S. Simmons Engineering Limited | Radstock | 1976 |
| C.S. Tractors Limited | | 1993 |
| C.S.E.A. Limited | Newcastle Upon Tyne | 1985 |
| C.S.I. Printing Ltd | Basingstoke | 2024 |
| C.S.K. Welding Ltd | Holmfirth | 2025 |
| C.S.K.L Limited | Stoke Golding | 2018 |
| C.S.L. Engineering Limited | Liverpool | 1990 |
| C.S.L. Industrial Limited | Retford | 1998 |
| C.S.M. Jewellery Service Ltd | Watford | 2025 |
| C.S.R. Engineering Group Limited | Nottingham | 2017 |
| C.S.S. Engineering Limited | Grantham | 1993 |
| C.T. Butler Ltd | Sandy | 2017 |
| C.T. Home Improvements & Freight Transport Ltd | Swansea | 2021 |
| C.T. Paper Sales Limited | Cannock | 1992 |
| C.T. Production Limited | Poole | 1982 |
| C.T. Strangeways Limited | Rye | 1977 |
| C.T.C. Precision Engineering Limited | Bath | 1986 |
| C.T.M Furniture Ltd | Gillingham | 2024 |
| C.T.M. (U.K.) Ltd. | Barnsley | 1999 |
| C.T.M. Equipment Limited | Barnsley | 2001 |
| C.T.R. Plastics Limited | Lancashire | 2003 |
| C.T.W. Hardfacing Limited | Sheffield | 1972 |
| C.U. Aircraft & Maintenance Ltd | Cambridge | 2025 |
| C.U.M.E Ltd | London | 2024 |
| C.V. Instruments Limited | Sheffield | 1971 |
| C.V. Labels Limited | Irvine | 1989 |
| C.V.Brickwork Ltd | Southam | 2025 |
| C.V.Flynn Ltd | Sale | 2025 |
| C.W. Architectural Interiors Limited | Sutton Coldfield | 1999 |
| C.W. Cheney & SON Limited | Birmingham | 1982 |
| C.W. Cheney Limited | | 1982 |
| C.W. Partitions & Floors Limited | Sunderland | 2008 |
| C.W. Sellors (Gold and Silversmiths) Limited | Liverpool | 1988 |
| C.W. Spinnings Limited | Tipton | 2006 |
| C.W.F. Poulten Limited | Southampton | 1971 |
| C.W.Fields & SON Limited | Epworth | 1962 |
| C.W.S (NI) Ltd | Dungannon | 2013 |
| C.Wild(Oldham)Limited | Chedderton | 1959 |
| C.Wilson Joinery&Building Ltd | Oldham | 2024 |
| C/L Refurbishments Ltd | Wolverhampton | 2022 |
| C/M Bakery Limited | London | 2013 |
| C02 Drinks Ltd | Harlow | 2010 |
| C13 Professional Yacht Service Ltd | Castleford | 2026 |
| C18 Group Ltd | London | 2025 |
| C2 Air Conditioning Ltd | Bath | 2013 |
| C2 Aviation Limited | London | 2013 |
| C2 Construction & Fabrication Ltd | Stoke-On-Trent | 2023 |
| C2 Construction Limited | Stoke On Trent | 2005 |
| C2 Group of Companies Ltd | Kensworth, Dunstable, | 2020 |
| C2 Signs & Print Ltd | Kensworth, Dunstable, | 2024 |
| C2 Technology UK Ltd | London | 2021 |
| C25 Furniture Limited | Chatham | 2020 |
| C25 Ltd | Banbridge | 2025 |
| C2C LAB Ltd | London | 2022 |
| C2K Upholstery Limited | Batley | 2010 |
| C2R-FAST Limited | Hereford | 2009 |
| C3 Engineering Limited | Dereham | 2001 |