| X-Rite Ltd. | Stockport | A rating |
| X.AI LONDON LTD | London | A rating |
| X2X Limited | London | A rating |
| X4 Group Ltd | London | A rating |
| XAAR Technology Ltd | Cambridge | A rating |
| Xactly Limited | London | A rating |
| Xanadu Consultancy Limited | London | A rating |
| XBP EUROPE LIMITED | Egham | A rating |
| XCap Ecosystem Ltd | London | A rating |
| XCD HR | Basingstoke | A rating |
| Xceedance Limited | London | A rating |
| Xcelentra Financial Services Ltd | Milton Keynes | A rating |
| Xebia UK Limited | London | A rating |
| Xero (UK) Limited | Milton Keynes | A rating |
| Xerox Limited | Uxbridge | A rating |
| Xiaomi Technology UK Limited | London | A rating |
| XIX Management Limited | London | A rating |
| XL CATLIN SERVICES SE T/A 'AXA XL' | LONDON | A rating |
| XML Ltd | London | A rating |
| XMOS Limited | Bristol | A rating |
| Xn Global Systems Ltd | Salford | A rating |
| Xodus Group Limited | ABERDEEN | A rating |
| Xoople UK Ltd | Manchester | A rating |
| Xoriant UK Limited | London | A rating |
| Xorlogics Ltd. | London | A rating |
| xpate Ltd | London | A rating |
| XPO Supply Chain UK Limited | Northampton | A rating |
| Xurrent Software UK Ltd | London | A rating |
| XY Capital Europe Limited | London | A rating |
| XY Sense UK Limited | Cheshire | A rating |
| Xylem Water Services Ltd | Nottingham | A rating |
| Yahoo-UK Limited | London | A rating |
| Yakult UK Limited | Chiswick | A rating |
| Yale University Press London | London | A rating |
| Yamaha Music Europe GmbH (UK) | Milton Keynes | A rating |
| Yamato Scale Dataweigh (UK) Ltd | Leeds | A rating |
| Yamato Transport Europe B.V. | Hounslow, | A rating |
| YAMAZAKI MAZAK (UK) LIMITED | WORCESTER | A rating |
| Yang Ming (UK) Limited | Romford | A rating |
| YAPIARTI LTD | London | A rating |
| Yara UK Limited | Grimsby | A rating |
| Yardi Systems Limited | Milton Keynes | A rating |
| Yardley of London Ltd | Windsor | A rating |
| YASA Limited | Oxford | A rating |
| Yash Technologies Europe Ltd | London | A rating |
| Yazaki Europe Limited | Basildon | A rating |
| Yellowbrick Data UK Limited | London | A rating |
| YELLOWFIN EMEA LTD | MILTON KEYNES | A rating |
| Yelp UK Limited | London | A rating |
| Yexle Limited | Milton Keynes | A rating |
| Yext Limited | London | A rating |
| YKK Europe Limited | London | A rating |
| YL I Limited | London | A rating |
| YMCA Indian Student Hostel | London | A rating |
| YMU Group Services Limited | London | A rating |
| Yokogawa UK Limited | Runcorn | A rating |
| Yolo Technology Limited | London | A rating |
| Yonder Consulting Limited | London | A rating |
| Yondr Group Limited | London | A rating |
| Yonex UK Ltd | London | A rating |
| Yoplait UK Limited | Uxbridge | A rating |
| York Bioanalytical Solutions Limited | York | A rating |
| Yoshino & Co., UK Ltd. | London | A rating |
| Yotel Limited | London | A rating |
| Yotpo UK Ltd | London | A rating |
| YouGov Plc | London | A rating |
| Young Living Europe Ltd | LONDON | A rating |
| Youwe UK Ltd | Leeds | A rating |
| Yovant Ltd | Harrow | A rating |
| YTL Developments (UK) Limited | Bath | A rating |
| Yuanda (UK) Co. Ltd | London | A rating |
| Yudo UK | Ross-on-Wye | A rating |
| YUGO STUDENTS (UK) LIMITED | Bristol | A rating |
| Yuken Europe Ltd | Liverpool | A rating |
| YUM! III (UK) LIMITED | St Albans | A rating |
| Yunex Limited | Christchurch | A rating |
| YUNFEI LIMITED | Tiptree | A rating |
| Yura Corporation UK Ltd | Lutterworth | A rating |
| Yusen Logistics (UK) Ltd | Northampton | A rating |
| Yushin Automation Limited | Bromsgrove | A rating |
| ZAFIN LABS UK LTD | LONDON | A rating |
| Zagreb-Montaza | Edinburgh | A rating |
| Zaizi Limited | London | A rating |
| Zakapps Software Limited | Caldecotte; Milton Keynes | A rating |
| Zalaris UK Ltd | Weybridge | A rating |
| Zanders (UK) Ltd | London | A rating |
| ZAP Technology Limited | London | A rating |
| Zapp Group Limited | London | A rating |
| ZappiStore Ltd | London | A rating |
| Zaria Group UK Limited | London | A rating |
| Zayo Group UK Limited | London | A rating |
| ZDF German TV | London | A rating |
| Zebra Pen (UK) Ltd. | Runcorn | A rating |
| Zebra Technologies Europe Limited | Bourne End | A rating |
| Zee Entertainment UK Limited | Middlesex | A rating |
| Zeeco Europe Limited | Rutland | A rating |
| ZEEKO LTD | COALVILLE | A rating |
| Zeepay JV UK | London | A rating |
| Zeidler Legal Services (UK) Limited | London | A rating |
| Zelle International LLP | London | A rating |
| Zema Services UK Limited | Altrincham | A rating |
| ZEN-NOH | London | A rating |
| Zendesk UK Ltd | London | A rating |
| ZeniMax Europe Limited | London | A rating |
| Zenith Bank (UK) Limited | London | A rating |
| Zenith UK (Media) Limited | London | A rating |
| Zenium Technology Partners Limited | London | A rating |
| Zenkyoren Europe Limited | London | A rating |
| Zennar Limited | Saltash | A rating |
| Zeno Communications (UK) Limited | London | A rating |
| Zenoss UK Limited | Coventry | A rating |
| Zensar Technologies (UK) Ltd | London | A rating |
| Zensho Foods UK LIMITED | London | A rating |
| Zentiva Pharma UK Limited | Guildford | A rating |
| Zeotap UK Limited | London | A rating |
| Zepp Health UK Limited | Reading | A rating |
| Zeren Search Ltd | London | A rating |
| Zero Proof International Limited | Rickmansworth | A rating |
| ZeroAvia Ltd | Cirencester | A rating |
| Zerofox UK Ltd. | London | A rating |
| Zerolatency UK Limited | Guildford | A rating |
| ZF Automotive UK Limited | Solihull | A rating |
| ZF Services UK Limited | Nottingham | A rating |
| ZG Lighting Limited | Spennymoor | A rating |
| Zhero Limited | London | A rating |
| Zhuzhou CRRC Times Electric UK Innovation Center | Birmingham | A rating |
| ZIEBE LIMITED | Aylesbury | A rating |
| Ziehl-Abegg UK Ltd | Chelmsford | A rating |
| Ziff Davis International Ltd | London | A rating |
| Zifo Technologies Ltd | Southport | A rating |
| Zigguratum Limited | Woking | A rating |
| Zilliant Limited | London | A rating |
| Zinnov UK Private Limited | LONDON | A rating |
| Ziton Ltd | London | A rating |
| Zoe Limited | London | A rating |
| Zoetis UK Limited | Leatherhead | A rating |
| ZOLL Medical UK Limited | Cheshire | A rating |
| ZoomInfo UK LTD | London | A rating |
| Zoomo London Ltd | London | A rating |
| Zoox Labs Ltd | Banbury | A rating |
| Zotefoams PLC | Croydon | A rating |
| ZPMC UK Limited | Liverpool | A rating |
| ZS Associates International Inc. | London | A rating |
| Zscaler UK Ltd | London | A rating |
| ZTE (UK) LIMITED | Slough | A rating |
| Zuffa UK Limited | London | A rating |
| Zuken Group Limited | Bristol | A rating |
| Zuora UK Limited | London | A rating |
| Zurich Insurance Group | Swindon | A rating |
| ZVC UK Ltd | London | A rating |
| Zvilo Limited | London | A rating |
| Zwift UK Limited | London | A rating |
| Zycus Infotech Private Limited | Harrow | A rating |
| ZyXEL Communications UK Ltd | Wokingham | A rating |