The government has spent £90 million on a key section of its Digital Britain plan, around sharing IT infrastructure for websites, without producing any measurement of the benefit.

That is according to the National Audit Office, which said in a report published today that it "cannot conclude" that the taxpayer is "securing value for money".

As part of the Digital Britain initiative, the government is attempting to deliver all services online, with its Directgov, and Government Gateway websites as the central focus.

The NAO said it was "crucial" that the Government Digital Service (GDS), established in March to deliver government services digitally, "builds in the right mechanisms to achieve value for money as it plans the future of digital shared infrastructure and services".

Amyas Morse, head of the NAO, said: "It is a good thing that people visited the two main government websites some 200 million times last year. However, it's still unclear what benefits have been achieved and at what cost."

The report does conclude, however, that Directgov, and Gateway have likely delivered some cost savings through the reuse of common infrastructure. They have also helped citizens and businesses to access information in a more organised way.

The sites were intended to help replace the thousands of portals in place. Since 2006, 1,526 government websites have been closed. But determining how successful the government has been in closing websites has proved difficult, the NAO said, because the baseline numbers were based on an estimate and targets have changed over time. Additionally, the government was unsure at the start how many sites it operated.