| Lyco Group Limited | Guildford | A rating |
| LYNQ LIMITED | FAREHAM | A rating |
| LyondellBasell Industries NV | Lonon | A rating |
| Lyra Health International Limited | London | A rating |
| Lyst Ltd | London | A rating |
| M & G PlC | London | A rating |
| M Moser Associates Ltd | London | A rating |
| M-Solv Ltd | Witney | A rating |
| M.F. Certus D.O.O. | Stoke On Trent | A rating |
| M.O. Tourist Co., Ltd. | Burnaston | A rating |
| M&C Saatchi PLC | London | A rating |
| M10 Edge Ltd | Stevenage | A rating |
| M3 (EU) Limited | London | A rating |
| M7 REAL ESTATE LTD | London | A rating |
| Mabanaft Limited | London | A rating |
| MacAlister Elliot & Partners Limited | Lymington | A rating |
| MacDermid Performance Solutions Services Ltd | Woking | A rating |
| Macduff Shellfish | Peterhead | A rating |
| Mace Ltd | London | A rating |
| Macfarlane Media Limited /The Media Image | London | A rating |
| Machnet Medical Robotics (UK) Ltd | London | A rating |
| MacIntyre Hudson LLP | Milton Keynes | A rating |
| Mackintosh Limited | Lancashire | A rating |
| Macmillan Publishers International Limited | Basingstoke | A rating |
| Macquarie Group Services Australia Pty Ltd (UK Branch) | London | A rating |
| Macrae Group UK Limited | London | A rating |
| Macrobond Financial Ltd | London | A rating |
| Madiba Consulting UK Limited | Bexhill on Sea | A rating |
| Madic Technologies Limited | Guildford | A rating |
| Madison CF UK Limited | Cardiff | A rating |
| Madison International Realty UK Ltd | London | A rating |
| Madison Logic UK Limited | London | A rating |
| Madras Check UK Ltd | London | A rating |
| MAERSK LINE UK LIMITED | Liverpool | A rating |
| Maersk Logistics and Services UK Ltd | Liverpool | A rating |
| Maersk Tankers UK Limited | London | A rating |
| Magellan Aerospace (UK) Ltd | Wrexham | A rating |
| Magentus Software Limited | Mansfield | A rating |
| MAGIC SOFTWARE SERVICES LTD | LONDON | A rating |
| Magmatic Games Ltd | London | A rating |
| Magna Exteriors (Liverpool) Limited | Liverpool | A rating |
| Magnasoft Europe Ltd | London | A rating |
| Magnet Limited | Darlington, | A rating |
| Magnetar Financial (UK) LLP | London | A rating |
| Magnit Global UK Limited | Chesire | A rating |
| Magnite Limited | London | A rating |
| Magnum ICC UK Limited | Kingston Upon Thames | A rating |
| Magus Research Limited T/A Crownpeak | London | A rating |
| Mahindra Advanced Design Europe (MADE) | Banbury | A rating |
| MAHLE Industries UK Ltd | Northampton | A rating |
| Mahou, S.A. | London | A rating |
| Maidsafe.NET Ltd | Glasgow | A rating |
| Maier UK LTD | Burntwood | A rating |
| Main Capital Partners UK LTD | London | A rating |
| Mainichi Newspapers of Japan | London | A rating |
| Mainstreamtek UK Ltd | Uxbridge | A rating |
| MAISON SUZU CO., LTD. | London | A rating |
| Majesco UK Limited | London | A rating |
| Major League Baseball Europe Limited | London | A rating |
| MAK-SYSTEM GROUP LIMITED | London | A rating |
| Make Limited | London | A rating |
| Makin Metal Powders (UK) Ltd | Rochdale | A rating |
| Makita (UK) Limited | Milton Keynes | A rating |
| Makita Manufacturing Europe Ltd | Telford | A rating |
| Makosi UK Ltd | London | A rating |
| Malander UK Limited | London | A rating |
| Malayan Banking Berhad | London | A rating |
| MALAYSIA AIRLINES BERHAD | LONDON | A rating |
| Malaysia Tourism Promotion Board | London | A rating |
| Malca-Amit UK Limited | London | A rating |
| Mallaghan Engineering Ltd | Dungannon | A rating |
| Malt Community Ltd | London | A rating |
| Malvern Panalytical Limited | Malvern | A rating |
| Mammoet (UK) Ltd | Wallsend | A rating |
| Man Capital LLP | London | A rating |
| MAN CORPORATION LIMITED | LONDON | A rating |
| Man Group Services Limited | London | A rating |
| Management Solutions Europe UK Limited | London | A rating |
| Manchester United Football Club Limited | Manchester | A rating |
| Mandarin Oriental Hyde Park Ltd | London | A rating |
| Manhattan Associates Limited | Wokingham | A rating |
| Manheim Limited | Leeds | A rating |
| Manitowoc Crane Group (UK) Ltd | Gawcott | A rating |
| MANN+HUMMEL (UK) Ltd | Wolverhampton | A rating |
| Mannaz A/S | London | A rating |
| Manolo Blahnik International Limited | London | A rating |
| Manpower UK Limited | Uxbridge | A rating |
| Manteio Capital UK Limited | London | A rating |
| Manulife Investment Management (Europe) Ltd | London | A rating |
| Mapbox UK Ltd | London | A rating |
| Mapei UK Ltd | Halesowen | A rating |
| Mapfre Re Compania De Reaseguros SA | London | A rating |
| Maples and Calder | London | A rating |
| Mapletree UK Management Ltd | London | A rating |
| MAPP Digital UK Ltd | London | A rating |
| Maptek Ltd | Edinburgh, | A rating |
| MARA LABS UK LIMITED | London | A rating |
| MARAFIE CONSULTANCY UK LTD. | Stockport | A rating |
| Marathon Capital Ltd | London | A rating |
| Marathon Trading and Supply Services Limited | London | A rating |
| Marble Bar Asset Management LLP | London | A rating |
| Marcura UK Limited | Worthing | A rating |
| Marelli Automotive Systems Europe plc | Llanelli | A rating |
| Marex Group Plc | London | A rating |
| Margaret Howell Limited | London | A rating |
| Margo Consulting Ltd | London | A rating |
| MariaDB UK Limited | London | A rating |
| Mariage Freres Royaume Uni | London | A rating |
| Mariana UFP LLP | London | A rating |
| Marine Stewardship Council | London | A rating |
| Marine Systems Technology Ltd | Winsford | A rating |
| Mariner Europe Limited | London | A rating |
| MARIONETE LIMITED | LONDON | A rating |
| Maritime Developments Limited | Aberdeen | A rating |
| Maritime Insights & Intelligence Limited t/a Lloyd's List Intelligence | London | A rating |
| Maritime Ventures UK Ltd | London | A rating |
| Mark Roberts Motion Control Limited | Blindley Heath | A rating |
| Markel International Services Limited | London | A rating |
| Marken Limited | Feltham | A rating |
| Markes International Ltd. | Bridgend | A rating |
| MARKET NEWS LIMITED | LONDON | A rating |
| Market Securities LLP | London | A rating |
| MarketAxess Europe Ltd | London | A rating |
| Marketing Options Limited | Surrey | A rating |
| MarketsandMarkets Limited | North Harrow | A rating |
| MarkitSERV Ltd. | London | A rating |
| Marks and Clerk LLP | London | A rating |
| Marks and Spencer Group Plc | London | A rating |
| Marktlink North UK M&A Limited | Manchester | A rating |
| Marposs Limited | Coventry | A rating |
| Marqeta UK Ltd | London | A rating |
| Marquis Technologies Limited | London | A rating |
| Marr Contracting International Limited | London | A rating |
| Mars Advisors Limited | London | A rating |
| Mars Food UK Limited | Slough | A rating |
| Mars Food UK Limited | Melton Mowbray | A rating |
| Mars Hospitality (UK) Limited | Invergarry | A rating |
| Mars Information Services, a division of Mars Wrigley Confectionery UK Limited | Slough | A rating |
| Mars Petcare UK | Melton Mowbray | A rating |
| Mars Wrigley Confectionery UK Limited | Slough | A rating |
| Marsh Services Ltd | London | A rating |
| Marshall Amplification Plc | Milton Keynes | A rating |
| Marshall Wace Asset Management Limited | London | A rating |
| Martifer UK Limited | London | A rating |
| Martin Brudnizki Design Studio | London | A rating |
| Martin Collins Enterprises Ltd | Lambourn Woodlands | A rating |
| Martin-Baker Aircraft Company Limited | Higher Denham, near Uxbridge | A rating |
| Martin-Brower UK Ltd | Hemel Hempstead | A rating |
| Martinez Otero UK, Ltd | London | A rating |
| Marubeni Europe plc | London | A rating |
| MARUGAME UDON (EUROPE) LIMITED | Bristol | A rating |
| MARUSHIN UK LTD T/A FELT Bakery | London | A rating |
| MARUWA EUROPE LTD | ASHFORD | A rating |
| Marvelous Europe Ltd | Aylesbury | A rating |
| Mary Quant Limited | London | A rating |
| MAS INTIMATES UK LIMITED | Herts | A rating |
| Masdar Offshore Wind UK Limited | London | A rating |
| Maserati GB Limited | Slough | A rating |
| Massilly UK Limited | Swansea | A rating |
| Masstock Arable (UK) Limited | Cheltenham | A rating |
| Mastek (UK) Limited | Reading | A rating |
| Mastek Systems Company Limited | London | A rating |
| Mastercard UK Management Services LTD | London | A rating |
| MasterControl Global Ltd | Basingstoke | A rating |
| Masuri Group Ltd | Winchester | A rating |
| Matalan Retail Ltd. | Liverpool | A rating |
| MATCH Hospitality AG | Cheadle | A rating |
| Match.com International Limited | London | A rating |
| Matiere UK Ltd | Brackley | A rating |
| Matilock UK Ltd t/a MetaMap | London | A rating |
| Matrix Machine Tool (Coventry) Ltd | Coventry | A rating |
| MATRIX RENEWABLES UK LIMITED | London | A rating |
| MATRIX-IFS UK LTD | London | A rating |
| Mattel UK Limited | Slough | A rating |
| Matthews Environmental Solutions Limited | Hyde | A rating |
| Maui Jim UK Ltd | Guildford | A rating |
| Mauve Corporate Systems UK Limited | London | A rating |
| Maven Securities Holding Limited. | London | A rating |
| Mavenir Systems Limited | Reading | A rating |
| Mavens Consulting Limited | London | A rating |
| Mavens Consulting Limited | Richmond | A rating |
| MAVERIC NXT LIMITED | London | A rating |
| Maxell Europe Limited | Slough | A rating |
| MAXIMUS UK Services Ltd | Lewes | A rating |
| Maxis GBN | London | A rating |
| Maxis Investments Limited | London | A rating |
| MAXMARA LTD | LONDON | A rating |
| Maxwell Food Products Pty Limited | Leeds | A rating |
| Maxwell Geosystems UK Ltd | London | A rating |
| Maya HTT UK Ltd | Derby | A rating |
| Maya Technologies Limited | London Heathrow | A rating |
| Mayborn (UK) limited | Newcastle Upon Tyne | A rating |
| Mayer Brown International LLP | London | A rating |
| Mayfair Midco Ltd | London | A rating |
| Mayo Clinic (UK) Ltd | London | A rating |
| Mayo Clinic Healthcare LLP | London | A rating |
| Mazda Motors UK Limited | Dartford | A rating |
| Maze.Design Limited | London | A rating |
| Mazlum London Limited | London | A rating |
| MAZZOLENI ART LIMITED | London | A rating |