Two-thirds of government departments are "flunking" the challenge of moving online effectively and endangering Tony Blair's commitment to deliver 100% of public services over the internet by 2005, a survey claims.

Internet consultancy Forrester Research graded the operations of 14 government departments from A to E - their average D.

Among the worst offenders were the crown prosecution service, Department of Social Security, customs and excise and office of national statistics which all scored E grades. The best were the inland revenue, Department of Trade and Industry, and the Department for Education and Employment, but they only gained C grades.

Deep seated cultural issues and unwieldy processes are the most common reasons blamed by leading technology providers who contributed to the report.

"The UK government's current strategy for delivering online services fails to make the grade," said Forrester analyst Caroline Sceats. "The technology exists to achieve the 2005 targets, but the reality is that the government won't be able to deliver."

Firms like Microsoft, Oracle and IBM said departments had to build external partnerships with organisations outside the public sector if they are to improve.

The figures will be a blow to the government which on Wednesday appointed a former inland revenue chief, Andrew Pinder, as its new e-envoy. "While not wishing to denigrate Mr Pinder's strong abilities it appears there was a big opportunity to appoint someone from the commercial sector to drive this through," said Ms Sceats.

Despite the criticism the government has made several positive strides in the e-commerce arena and remains confident of hitting its 2005 target. Information portal UKOnline has proved a popular source of government information and the government estimates that 40% of its services are already on the web.