| Müller Dairy UK Ltd | Market Drayton |
| MacRoberts Solicitors | Glasgow |
| Maecenata Management GmbH | München |
| The Mail on Sunday | London |
| Maitland Sponsorship Consultancy | Liphook |
| Majestic Wine Warehouses Ltd | Watford |
| Making Music | London |
| Malaysia Tourism Promotion Board | London |
| The Malcolm Clark Consultancy Ltd | Pulborough |
| The Mall | London |
| Man Group PLC | London |
| Manby & Steward | Wolverhampton |
| Manchester Airport | Manchester |
| Manchester City Football Club | Manchester |
| Manchester Evening News | Manchester |
| M&C Saatchi Sport & Entertainment Ltd | London |
| M and M Direct | Leominster |
| Manpower UK | Uxbridge |
| Maplin Electronics | Rotherham |
| Margaux Matrix (UK) Ltd | Godalming |
| Marketing Communication Consultants Association (MCCA) | London |
| Marks & Spencer Group Plc | London |
| Marlow Foods Ltd | Stokesley |
| Mars UK (Confectionery) | Melton Mowbray |
| Mars UK (Pedigree Petfoods Division) | Slough |
| Marshall Group of Companies | Cambridge |
| Marshalls Plc | Elland |
| Marston's Plc | Wolverhampton |
| Martin Currie Investment Management Ltd | Edinburgh |
| MasterCard Europe | London |
| Material Marketing & Communications Ltd | Glasgow |
| Mattel UK Ltd | Maidenhead |
| Maximise Marketing & Events Ltd | Glasgow |
| Maximuscle Ltd | Hemel Hempstead |
| Mayer Brown International LLP | London |
| Mazda Motors (UK) Ltd | Dartford |
| MBA Ltd | Tadcaster |
| MBNA Europe Bank Ltd | Chester |
| McAfee | Slough |
| MCC | London |
| McCain Foods (GB) Ltd | Scarborough |
| McCormick (UK) Ltd | Aylesbury |
| McDonald's Restaurants Ltd | London |
| McNeil Nutritionals Ltd | London |
| MDH Communications Ltd | London |
|
MEC:Access | London |
| Mecenat - Association for Corporate Support of the Arts | Tokyo |
| MediaCom | London |
| Mediadata Ltd | Surbiton |
| The Mentholatum Co Ltd | East Kilbride |
| Mentzendorff & Company Ltd | London |
| Mercedes-Benz (UK) Ltd | Milton Keynes |
| Meridian Lifts | Poole |
| Merrill Lynch Investment Managers | London |
| Metabo UK | Southampton |
| Metro | London |
| Metro Ecosse | Edinburgh |
| Metro Radio Ltd | Newcastle upon Tyne |
| Metzeler Racetec | Burton-on-Trent |
| MHS Homes | Chatham |
| Michael Kay Associates Ltd | Sherborne |
| Microsoft Ltd | Reading |
| The Mid-Counties Co-operative | Oxford |
| Midland Newspapers Ltd | Coventry |
| Mike Burton Group Ltd | Gloucester |
|
Millennium Stadium | Cardiff |
| Miller Construction UK | Edinburgh |
| Mini-Basketball England (MBE) | Northampton |
| The Mirror | London |
| Mitchells & Butlers PLC | Birmingham |
| Mitre Sports International Ltd | London |
| Mitsubishi Motors | Cirencester |
| Mizuno Corporation | Wokingham |
| MMC | London |
| Modern Hairdressing Group | Bradford |
| Modern Pentathlon Association of Great Britain (MPAGB) | Bath |
| Moët Hennessy UK Ltd | London |
| Monarch Airlines Ltd | Luton |
| Monde | Weybridge |
| Moneysupermarket.com Group plc | Chester |
| The Morgan Crucible Company plc | Windsor |
| Morgan Stanley & Co Plc | London |
| Mornflake Oats Ltd | Crewe |
| Morphy Richards Ltd | Mexborough |
| Mothercare PLC | Watford |
| Motor Sports Association UK (MSA) | Slough |
| Motorola Ltd | Basingstoke |
| Mountaineering Council of Scotland (MCofS) | Perth |
| Muckle LLP | Newcastle upon Tyne |
| Mumtaz Food Industries Ltd | Bradford |
| Mundays LLP | Cobham |
| Murray International Holdings | Edinburgh |
| The Museums Association | London |
| Museums Galleries Scotland | Edinburgh |
| Museums, Libraries & Archives Council (MLA) | London |
| The Music & Media Partnership | London |
| MWM Sports Management Group | Holywood |
