| Kinkell Energy Limited | Laurencekirk | 2016 |
| Kinlochleven Power Ltd | Perth | 2016 |
| Kinlochteacuis Hydro Limited | Edinburgh | 2013 |
| Kinmel 1 C.I.C. | London | 2014 |
| Kinmel 2 C.I.C. | London | 2014 |
| Kinmuck Energy Limited | Aberdeenshire | 2020 |
| Kinnaird Hydro Limited | | 1972 |
| Kinsman Ltd | London | 2010 |
| Kintarbert Hydro Ltd. | Perth | 2011 |
| Kintore Hydrogen Limited | London | 2022 |
| Kintyre Renewable Energy Park Limited | Edinburgh | 2022 |
| KIP Water Hydro Limited | Lochgilphead | 2015 |
| Kirby Power Ltd | Reading | 2023 |
| Kirk Hill Wind Farm Limited | Redruth | 2014 |
| Kirkan Wind Farm Limited | Maidenhead | 2014 |
| Kirkby Battery Storage Ltd | Godalming | 2021 |
| Kirkgate Lane Solar Farm Limited | Exeter | 2021 |
| Kirkley Power Distribution Services Limited | Lowestoft | 2012 |
| Kirkstone Energy Limited | Kendal | 2015 |
| Kirkton Energy Limited | Forfar | 2024 |
| Kirkton Wind Farm Limited | Edinburgh | 2020 |
| Kislingbury Energy Limited | Milnthorpe | 2025 |
| Kislingbury M1 Solar Limited | Gatwick | 2014 |
| Kitch Nova Ltd | London | 2025 |
| Kitland Solar Farm Limited | London | 2023 |
| Kitwell Energy Storage Park Limited | London | 2023 |
| Kiwi Power ES B Limited | London | 2017 |
| Kiwi Power International Limited | London | 2015 |
| Kixley Energy Limited | Lapworth, Solihull | 2021 |
| KJ Civils Ltd | Sheffield | 2025 |
| KJN Air Conditioning Ltd | Whaley Bridge | 2026 |
| KJT Technologies Limited | Richmond | 2025 |
| KKS Property Solutions (UK) Ltd | London | 2025 |
| KL Energy Limited | King'S Lynn | 2024 |
| Klaen Health Ltd | Witney | 2025 |
| Klamat Ltd | London | 2014 |
| Klams Group Ltd | Buntingford | 2026 |
| KLB Energy Co Limited | Blairgowrie | 2016 |
| Klimatech Controlling Your Environment Ltd | Snettisham | 2021 |
| Klimatech Limited | Kings Lynn | 2008 |
| Klingenburg U.K. Ltd | Margate | 2013 |
| KLT Renewables Limited | King'S Lynn | 2017 |
| KM Electric and GAZ Limited | London | 2022 |
| KM GAS & Services Ltd | Newry | 2010 |
| KM Renewable Energy Ltd | Birmingham | 2014 |
| Kmac Associates Limited | Belfast | 2016 |
| Kmec Electrical Services Ltd. | March | 2012 |
| Kmechanical Ltd | Musselburgh | 2025 |
| KN Civils Ltd | Barnet | 2018 |
| KN Energy Centre Ltd | Liverpool | 2022 |
| KN Energy Solutions Limited | Egham | 2024 |
| Knabs Ridge Wind Farm Limited | Swindon | 2005 |
| Knappagh Renewables Ltd | Armagh | 2020 |
| Knapton Solar Ltd | London | 2025 |
| KNE Limited | Thirsk | 2016 |
| Knepp Energy Limited | Knepp Grinstead | 2013 |
| Knightbell Limited | Milton Keynes | 1989 |
| Knights Air Ltd | Stock | 2025 |
| Knights Commissioning Services Limited | Reading | 1994 |
| Knightshayes Estate Energy Ltd | Tiverton | 2011 |
| Knockavannon Ltd | Belfast | 2013 |
| Knockavoe Renewables Limited | Belfast | 2016 |
| Knockkippen Wind Energy Limited | Edinburgh | 2023 |
| Knockshinnoch Wind Energy 2021 Limited | Berkeley | 2021 |
| Knockshinnoch Wind Energy 2022 Limited | London | 2022 |
| Knockshinnoch Wind Energy Limited | Berkeley | 2020 |
| Knockworthy Solar Park Limited | London | 2012 |
| Knottingley Power Limited | London | 2006 |
| Knowl Green Solar Park Limited | Shepton Mallet | 2021 |
| Knowsley Electric Charging Ltd | Liverpool | 2022 |
| Knowsley Energy Recovery Limited | Salford Quays | 2009 |
| Knowsley NET Zero Ltd | London | 2021 |
| Knox Utility Ltd | Manchester | 2025 |
| Knoydart Renewables Limited | Mallaig | 1999 |
| KOE Group Ltd | Wallington | 2022 |
| Koehler Renewable Energy UK Limited | Glasgow | 2021 |
| Kompair Ltd | London | 2022 |
| Kona Asset 2 Limited | London | 2021 |
| Kona Asset 3 Limited | London | 2022 |
| Kona Asset 4 Limited | London | 2022 |
| Kona Asset 5 Limited | Towcester | 2024 |
| Kona Asset 6 Limited | Towcester | 2024 |
| Kona Asset 7 Limited | Towcester | 2024 |
| Kona Asset 8 Limited | Towcester | 2024 |
| Kona Energy Limited | London | 2021 |
| Konarkinc Renewables Ltd | London | 2025 |
| Konik Ltd | Cheltenham | 2020 |
| Konnect Technical Limited | Tamworth | 2021 |
| Konnect Utilities Limited | Wood Lane | 2016 |
| Kontotronics Limited | London | 2003 |
| Kool Control Ltd | Bootle | 2019 |
| Kool Touch Limited | Aylesbury | 2014 |
| Koolair Hvac Ltd | Slough | 2023 |
| Kore Electrics Limited | Reading | 2015 |
| Koventures Ltd | Woolwich, London | 2026 |
| KPB Electrical Services Ltd | Manningtree | 2026 |
| KPF EV Limited | Motherwell | 2026 |
| Kpmd & Co Limited | Sunderland | 2015 |
| KPP132 Limited | London | 2013 |
| KPP141 Limited | London | 2014 |