I believe the Tories are basing their figure on calculations made during independent research for a paper published a year or so ago.
The total current and future impact of the abolition of Advanced Corporation Tax (ACT) relief was calculated by Terry Arthur, a fellow of the Institute of Actuaries, in a paper written for the professional body. Mr Arthur said: "What happened in 1997 represented an enormous and ongoing raid on the assets of UK company pension schemes. My research shows it would be very hard to justify an impact of less than �100 billion � and even �150 billion may still be a conservative estimate."
http://www.telegraph.co.uk/money/main.jhtml?xm l=/money/2006/10/15/ccliam15.xml
Terry Arthur BSc FIA
Fellow of the Institute of Actuaries
Fellow of the Pensions Management Institute
Visiting Fellow of the Institute of Economic Affairs
Visiting Fellow of University of Buckingham
Visiting Fellow of Westminster Business School
Adjunct Scholar of the Ludwig von Mises Institute
Director - Allianz Dresdner Second Endowment Policy Trust Plc
Director - SVM Global Fund plc
Exec Chairman, TKM Group Pension Scheme, 1996-2006
Director, Royal Mail Pension Trustees Ltd, 1998-2004
and contributor to The Libertarian Alliance - a non-partisan group fighting statism in all its forms and working for the creation of a truly free society.