David Blunkett has denied any wrong-doing in relation to the visa application of his ex-lover's nanny.
The inquiry into the Blunkett row could report next week
The Daily Mail has published Home Office letters to Leoncia Casalme, Kimberly Quinn's nanny.
They initially told her it could take up to a year to process her visa claim, but 19 days later said she could stay in the UK indefinitely.
But the Home Office says it was not unusual for straightforward visa claims to be processed quickly.
In Thursday's Daily Mail, Miss Casalme is reported as saying Mrs Quinn told her about her visa: "I'll see what I can do, I have a friend."
Mr Blunkett says he checked the application for permanent residence was filled in correctly but did not intervene to get it approved.
Speaking outside the UK Passport Office on Wednesday, he said the letters were genuine but proved nothing about his conduct.
"I wouldn't be standing here if I thought there was any doubt whatsoever about what I've done," he said.
Downing Street has reiterated the prime minister's support for his home secretary and hinted that a probe into his conduct in the visa affair could report next week.
In a statement, the Home Office said it had begun charging for processing most immigration
applications in August 2003.
"In the months in advance of that, to be in a position to deliver a
good service to applicants when charging began, the Home Office made
efforts to process existing applications as quickly as possible," it said.
was not unusual for straightforward cases to be dealt with within a
Conservative shadow home secretary David Davis said the statement raised more questions.
The fact that Miss Casalme's application could not be decided on initial consideration suggested it had not been a "straightforward case", he argued.
The Home Office's Permanent Secretary, John Gieve, has asked Sir Alan Budd to examine the handling of Miss Casalme's application for indefinite leave to remain.
Lib Dem spokesman Mark Oaten said Mr Blunkett was "innocent until proven guilty" but there was something "very unusual" about the visa application.
Immigration lawyer Philip Trott said it was "bizarre in the extreme" for the visa initial immigration unit to say it could not deal with an application only for it to be cleared 19 days later.
But some agencies recruiting foreign workers such as nannies and housekeepers have found it is quite common for residency applications to be processed early.
Job or children?
The latest developments came as it emerged Mrs Quinn, who is seven months pregnant, was admitted to hospital on Monday night amid the stress caused by the controversy.
There could be a legal battle over Mr Blunkett's status as a father of two children, one of whom is unborn.
Mr Blunkett and Mrs Quinn with Michael Parkinson and his wife Mary
In an appeal on Wednesday, Mrs Quinn's husband Stephen said: "I would like to seek an adjournment until such a time as our baby is born
and my wife has recovered from that."
BBC political editor Andrew Marr said Mr Blunkett would choose his rights as a father ahead of his political career but did not believe the situation would come to that.
Review under way
The letters published in the Daily Mail do not mention Mr Blunkett or indicate that he interfered in the process.
One sent to Miss Casalme on 23 April 2003 says her application cannot be decided immediately.
It says: "The waiting period for these cases is about 12 months at the moment..."
But a second letter dated 12 May tells Miss Casalme: "You can now remain indefinitely in the United Kingdom."
On Tuesday Mr Blunkett said he was repaying £180 to Parliament for the first class train ticket he gave to Mrs Quinn. He apologised for his "genuine mistake".
The Parliamentary Commissioner for Standards in Public Life is looking at the issue following a complaint.