Departments must "work closely" with the Government Digital Service to ensure the ambitious pan-Whitehall identity assurance target of 2016 can be met, The National Audit Office has said.
This is despite the fact the Verify identity assurance tool has so far had a shaky start. Last month a beta test of the tool drew many complaints from farmers attempting to use Defra's Common Agricultural Policy information services.
Labour has also called for a review of Verify if the service is not in a more stable position before the next government takes office. The programme is now "significantly behind" its original launch date of August 2012, it said.
Identity assurance is a key part of the digital-by-default agenda to enable users to conduct government transactions online.
GDS intends to introduce Verify to "more complex and high volume digital services over the coming years".
However, the dates for the majority of government services to start using the identity assurance service are yet to be confirmed.
In its briefing note to departments, the NAO said: "Departments will need to work closely with the GDS to ensure the delivery of identity assurance services which meet their requirements.
It added: "Departments need to understand the scope of the technical service and its impact on their responsibilities, security and risk appetite."
But sources say an identity skills shortage within departments could be a major obstacle for the programme, particularly as this is known to be an area which is "extremely difficult" to recruit for.
To date, the programme has cost £25m to design and develop a single, cross-government identity assurance service. GDS signed contracts with five providers in September 2013: Digidentity, Experian, Mydex, Post Office and Verizon. ®