The Government will face fresh questions over the loss of millions of voters' personal data amid evidence the debacle has helped fuel a massive slump in public confidence.
One poll showed those backing Labour's ability to handle economic problems had been more than halved to 28%, with just a quarter deeming Gordon Brown's administration "competent and capable".
And another gave the Tories a nine-point overall lead, its strongest position for 15 years, just weeks after Labour enjoyed an 11-point advantage in the same poll.
The revelation that two CDs containing the information, including bank details, had failed to reach the National Audit Office in London after being sent through HM Revenue and Customs' internal post system sparked fears they could fall into the hands of fraudsters.
The Opposition seized on the release of Whitehall emails about the transfer of 25 million individuals' personal details to pile further pressure on Chancellor Alistair Darling.
Tories said the exchanges cast fresh doubt on Mr Darling's claims that the loss of the database was down to a junior official ignoring proper procedures.
Meanwhile an urgent review of security at the London headquarters of the HMRC has been ordered after a journalist posing as a contractor gained access.
The Sun reporter said he "swanned around unchallenged" at HM Revenue and Custom's offices in Euston after being issued with a temporary security pass and had access to files.
An HMRC spokesman said: "This is a very serious breach of our building security.
"We are urgently reviewing the security measures in place at all of our premises."
