Culture Secretary Jeremy Hunt will appear before Lord Justice Leveson today in what is expected to be a key day of drama for the inquiry.
Mr Hunt is likely to be asked about what contact he authorised between his special adviser Adam Smith and Fred Michel, the head of public affairs for News Corporation in Europe.
He can also expect questions about whether he was the right person to decide in a quasi-judicial role whether Rupert Murdoch's multinational company should be allowed to take over the satellite broadcaster BSkyB.
Mr Hunt had asked for his appearance before Leveson to be brought forward after the inquiry released a cache of emails and text messages detailing a high level of contact between Mr Michel and Mr Smith.
They appeared to show News Corporation had received inside information about the Department for Culture, Media and Sport's handling of the bid from Mr Smith. The special adviser quit last month after admitting he went too far in acting as a point of contact for the company.
It is these emails and text messages which are likely to be a focal point of questioning by Robert Jay QC, lead counsel for the inquiry, as he seeks to establish how much the Culture Secretary knew about, and authorised, his special adviser's close relationship with Mr Michel.
Mr Hunt can also expect questions on whether he was right to accept responsibility for overseeing the takeover bid in a quasi-judicial role after previously revealing his support for the move.
Last week the inquiry published a memo he sent to Mr Cameron in November 2010 in which he appeared to be making the case for News Corp's bid to go ahead.
Weeks later the Business Secretary Vince Cable was stripped of the quasi-judicial responsibility after he told two undercover reporters from The Daily Telegraph he was seeking to block News Corp's attempt to buy the 61% of BSkyB which it did not already own, by referring the bid to regulators Ofcom.
He went on to tell the reporters in a secret recording that he had "declared war" on Mr Murdoch.
Prime Minister David Cameron has given the Culture Secretary his backing but warned that if anything arises from the inquiry that suggests the ministerial code might have been breached, he will call in his independent ethics adviser Sir Alex Allan or take immediate action himself.
A decision on whether Sir Alex should investigate the Culture Secretary's behaviour is expected shortly after Mr Hunt gives evidence.
Mr Hunt is due to appear before Leveson at 10am and is the only witness scheduled for the day.