Alastair Campbell wrongly accused Cherie Blair's lifestyle consultant of tipping off newspapers about the movements of the former prime minister's wife, the Leveson Inquiry heard today.
Tony Blair's former communications director said he had apologised to Carole Caplin, who has been told by police that her mobile phone was hacked by the News of the World.
Mr Campbell told the inquiry into press standards that he often wondered how stories got out about Mrs Blair when she was living in Downing Street.
He said he believed a story about Mrs Blair's pregnancy printed by the Daily Mirror in 1999 could have been obtained by phone hacking.
"During various periods of the time that we were in government, we were very, very concerned about how many stories about Cherie and Carole Caplin were getting out to different parts of the media," he said.
"I had no idea how they were getting out. In relation to not just Carole, and not just Cherie, but all of us who were involved in the government at that time, all sorts of stuff got out.
"Some of it may have got out because people who were within the government were putting it out there. Perhaps. That does happen.
"But equally there were all sorts of stories where you would just sit there scratching your head thinking, 'how the hell did that get out?'.
"I did, at times, directly accuse Carole Caplin of tipping off newspapers about what she was up to. I have since apologised because I now realise I was completely wrong."
He told the inquiry Ms Caplin said she was happy to write a letter to the inquiry giving more details.
The former No 10 communications chief added in a witness statement: "I have also never understood how the Daily Mirror learned of Cherie's pregnancy. As I recall it, at the time only a tiny number of people in Downing Street knew that she was pregnant.
"I have heard all sorts of stories as to how the information got out, but none of them strike me as credible."
Mr Campbell said he became suspicious that his own phone might have been hacked following a meeting with former Labour culture secretary Tessa Jowell.
"We set up the meeting via mobile phone, rather than through our offices. When we arrived at my house, where we had arranged to meet, a photographer was outside," he said.
Mr Campbell said his medical records were kept at the home of his former GP rather than in the surgery because of fears that the media would try to obtain them.
On occasions his bank and telephone company informed him that someone pretending to be him had attempted to "blag" access to his accounts.
"I have no way of knowing if this was a journalist or private detective working for one," he said.
He added: "I am aware of private information about Gordon Brown which was revealed through blagging.
"I have a close friend, a public figure not in politics, whose medical records were secured by a journalist through blagging."
He also said he had woken up in the middle of the night to find people going through his bins "on a couple of occasions".
Mr Campbell told the inquiry he had been contacted by Scotland Yard detectives from the Operation Weeting phone-hacking investigation who showed him references to himself and his partner in private investigator Glenn Mulcaire's notes.
He was also visited by officers from Operation Tuleta, the police inquiry into privacy intrusions other than phone hacking, who briefed him on computer hacking - although the former spin doctor stressed he was not told he was a victim.
Mr Campbell added: "(I was) also briefed on invoices they had found, that the Mirror had paid private investigators who were looking at me and Peter Mandelson at a certain point."
Mulcaire was jailed with Clive Goodman, the News of the World's former royal editor, in January 2007 after they admitted intercepting voicemail messages left on royal aides' phones.
A draft of Mr Campbell's witness statement was leaked at the weekend by Paul Staines, who blogs under the name Guido Fawkes.
The former Number 10 communications director told the inquiry today that he sent early versions of his statement to lawyers, former political colleagues and three journalists, but said he was confident none of them would have passed it on to Mr Staines.
Inquiry chairman Lord Justice Leveson has summoned Mr Staines to give evidence tomorrow about how he obtained the document.
Prime Minister David Cameron set up the Leveson Inquiry in July in response to revelations that the News of the World commissioned Mulcaire to hack murdered schoolgirl Milly Dowler's phone after she disappeared in 2002.
The first part of the inquiry, sitting at the Royal Courts of Justice in London, is looking at the culture, practices and ethics of the press in general and is due to produce a report by next September.
The second part, examining the extent of unlawful activities by journalists, will not begin until detectives have completed their investigation into alleged phone hacking and corrupt payments to police, and any prosecutions have been concluded.