Just 60 percent of those testing a new online tax returns service have been able to certify their identity using the government's new identity assurance scheme.
The government promises the scheme, dubbed 'GOV.UK Verify', will become the default way for citizens to certify they are who they say they are online.
It will be used to access all online government services that require proof of identity by 2016 and is currently being piloted by HM Revenue & Customs (HMRC) for its new online self-assessment tax returns service.
However GOV.UK Verity is currently shutting out about 40 percent of those trying to access it, according to a blog post on GOV.UK by the Government Digital Service (GDS).
"The trial has been going well. So far 3,700 people have successfully verified their identity using GOV.UK Verify as part of the trial. About 60 percent of visits by people attempting to verify their identity using GOV.UK Verify have been successful," GDS said.
This number is up from 42 percent earlier in the trial but the government eventually aims for 70 to 80 percent of people to use the service to certify their identity, ComputerworldUK understands.
GOV.UK Verify is being constantly tweaked and improved, with GDS recently expanding the number of data sources that can be used to validate users' identities.
The GDS explained: "We've been making improvements based on feedback and data throughout the trial so far. For example, HMRC has made some changes to the way users are told about the trial within the service."
The small-scale HMRC trial will close on 27 January, ahead of the 31 January deadline for tax returns, and will reopen in mid-February, the post added.
ComputerworldUK tested the new service and was able to register in about five minutes. However it seems some users are unable to use it due to problems with matching data such as credit card details and former addresses.
A public beta of GOV.UK Verify at another Whitehall department hit problems in October.
A number of individuals complained after finding themselves cut off from the new online service for Common Agricultural Policy payments because they were unable to certify themselves using the new scheme.
GDS has said GOV.UK Verify will be open to over 650,000 users by September and has promised to improve the service between now and then.
It has also said that those unable to use GOV.UK Verify, for example because they don't have a passport, will be offered alternative methods to certify their identity when accessing online services.
A recent Labour party report said GOV.UK Verify is "running significantly behind the initially committed schedule" and may need to be reviewed if the party takes office in May, if it is not in a more 'stable' position.
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