The Tories and the Lib Dems are calling for a second inquiry into the fast-tracking of a visa application for David Blunkett's ex-lover's nanny.
Reports of Mr Blunkett's relationship first appeared in August
Sir Alan Budd found a "chain of events" linked Mr Blunkett to Leoncia Casalme's indefinite leave to remain application, but he could not say exactly how.
Tory leader Michael Howard said "many questions" were left unanswered.
John Prescott said there was no need for a fresh inquiry as Mr Blunkett had been found guilty and had resigned.
On Tuesday, Sir Alan said the application for leave to remain in the UK made by Kimberly Quinn's nanny was processed in 52 days, 120 days faster than the average.
But he could not find evidence to show whether Mr Blunkett's intervention was intended to give special help for his then lover's nanny - or if he was raising the case as an example of poor departmental performance.
Sir Alan said he thought there had been no deliberate attempt to conceal or destroy evidence - even though a key fax from Mr Blunkett's office to IND had never been found.
Mr Howard said: "There does need to be another inquiry, a judge-led inquiry. There were so many questions that weren't answered.
"The worry has to do with the way government is conducted.
"What we have seen here is again what we saw in the Butler Inquiry - minutes weren't kept, faxes were lost, meetings took place and no records were kept of the meeting."
There was "deceit at the heart of government" which was not limited to the visa affair, he added.
Lib Dem home affairs spokesman Mark Oaten also said there was "a strong case for a judge-led judicial review".
"Next time it happens it may not be about a nanny and their visa. It may be about something even more important than that.
"So we do need to understand what took place and who was involved."
KEY E-MAILS - MAY 2003
"Just wondering if you have any update on the settlement (domestic worker) case I faxed through to you?"
Mr Blunkett's private secretary e-mails the Immigration and Nationality Directorate director general
"Sorted - she has been granted ILR - papers will be sent to her shortly. The case was in ICU so they pulled it out of the queue and made a decision - (no special favours, only what they would normally do - but a bit quicker)"
The IND director general's private secretary's reply
But Mr Prescott rejected suggestions a new probe was needed saying the report was conclusive.
"There was an intervention, it was fast-tracked and he resigned.
"He has been found guilty of the offence, it has been found that he had intervened."
Mr Prescott also defended the prime minister's prediction the former home secretary would be exonerated, saying "he expressed a judgement".
Mr Blunkett quit as home secretary last week after being told in advance of Sir Alan's findings.
In a statement, the ex-home secretary said he accepted the inquiry's findings.
He said he had told the truth throughout and had raised the nanny case as an example of unacceptable backlogs in the system.
Home secretary Charles Clarke said there would be new rules drawn up on how ministers should handle cases brought to their attention.