The £3bn contract to upgrade NHS computer systems had been "fraudulently concealed" from investors in American IT contractor Computer Sciences Corporation for years, according to a class action claim being brought by angry shareholders.

CSC, now face the possibility of litigation on two fronts – from shareholders and the British taxpayer. The group's existing NHS work is running years behind schedule and has racked up huge costs, much of which have yet to be divided between CSC and British taxpayers.

According to the class action complaint, brought on behalf of a number of investors led by a major Canadian fund, the Ontario Teachers' Pension Plan, as early as May 2008 CSC knew, through reports and testing, that Lorenzo (software package) was "dysfunctional and undeliverable".