Acounting firms:
PricewaterhouseCoopers
BDO
Grant Thornton UK LLP
Grant Thornton International 
Grant Thornton LLP (USA)

Baker Tilly
PKF
Goodman Jones

Mazars

Energy and Commodities:
ED & F Man
BG Group plc
Centrica plc
EDF Energy

E.On Ruhrgas

Nexen Petroleum

Qatargas

Santos
Twinings

Telecommunications:
Hutchison 3G
Virgin mobile

Retail:
Mothercare plc

Hugo Boss

Investment Banks and Companies:
Dresdner
Standard Bank
State Street Bank
Schroders
Brewin Dolphin
JP Morgan
Bank of New York
Deutsche Bank

Transport:
easyJet plc
bmi (now part of British Airways)
Eurostar

Government departments:

Bank of England

Highways Agency

National Audit Office

UK Bar Standards Council 

Magnox (Nuclear Decommissioning Authority)

Professional Accountancy Bodies:

Institute of Chartered Accountants of Bermuda (ICAB)

Cayman Islands Society of Professional Accountants (CISPA)

Institute of Chartered Accountants in England and Wales (ICAEW)

Association of Chartered Certified Accountants (ACCA)

Law firms:
Baker & Mackenzie
Slaughter & May

Leisure:

Manchester United