Adam Smith, the special adviser to the culture secretary, Jeremy Hunt, has resigned, saying he acted without the authority of his boss and that he had allowed the impression to be created of too close a relationship between News Corps and the Department for Culture, Media and Sport.

His resignation came an hour before Hunt was due to make a statement to MPs on Wednesday.

Emails published at the Leveson inquiry showed that News Corporation's public affairs director, Frédéric Michel, had been given inside information on ministerial thinking over the company's bid for BSkyB, including handing over commercially confidential information and repeatedly suggesting that Hunt wanted the bid to succeed.

In a statement, Smith said: "While it was part of my role to keep News Corporation informed throughout the BSkyB bid process, the content and extent of my contact was done without authorisation from the secretary of state. I do not recognise all of what Fred Michel said, but nonetheless I appreciate that my activities at times went too far and have, taken together, created the perception that News Corporation had too close a relationship with the department, contrary to the clear requirements set out by Jeremy Hunt and the permanent secretary that this needed to be a fair and scrupulous process.

"Whilst I firmly believe that the process was in fact conducted scrupulously fairly, as a result of my activities it is only right for me to step down as special adviser to Jeremy Hunt."

Labour is certain to ask whether Smith was really a lone operator and was, as he claims, acting without Hunt's permission.

It has already been established that Michel, in his emails, repeatedly refers to JH when in fact this was Adam Smith. However, on other occasions in the emails and texts it appears as though Michel's interlocutor is Hunt himself.

Michel also says in his witness statement that when he was speaking to Smith he was sure he was being given an account of the culture secretary's thinking. It is hard to think of a motive for Smith to give Michel an accurate account of Hunt's thinking that on the surface seems to be biased towards News Corp.

Under the ministerial code, the secretary of state is responsible for the actions of his special adviser.

The government offered the Commons statement after Labour requested that Hunt account for revelations at the Leveson inquiry about email exchanges with Rupert Murdoch's company and whether they were at odds with undertakings he gave to parliament.

Hunt had suggested he should be allowed to mount his defence at the Leveson inquiry, and that his hearing should be brought forward. He is not due to give evidence for four weeks, and in the modern political world, it seems implausible that he would be allowed to keep his job for that long without clear evidence that his actions were dramatically misrepresented by the emails released to the inquiry by Michel.

The culture secretary will be hoping he receives strong support from Conservative backbenchers, and has already insisted his contacts with the Murdoch organisation were formal and kept to a minimum. He has also indicated that the culture permanent secretary gave his special adviser permission to keep in touch with News Corp during the BSkyB bid process.

But senior former civil servants have said the permanent secretary would only have allowed formal contacts about process, and would not have granted permission to give insights into Hunt's thinking, or to work together to put forward a case likely to ensure the bid was waved through.

His supporters have insisted that he acted throughout on the advice of independent media regulators. However, Ofcom had recommended the bid should be referred to the Competition Commission. Hunt in discussion with Ofcom rejected that advice and said assurances granted by News Corp, including spinning off Sky News, made it possible for the bid to be waved through.