Jeremy Hunt spent five days in the US, holding meetings with News Corporation when Rupert and James Murdoch were first deciding whether to bid for Sky, official documents reveal.

Almost immediately after Hunt's trip, James Murdoch visited David Cameron in London, and privately told him that News Corp had agreed to switch its support to the Tories in the upcoming election. Hunt then became culture secretary in the victorious Tory government.

Hunt's officials at the Department for Culture, Media and Sport declined to comment on what Hunt had been doing at News Corp's headquarters in August 2009, a visit disclosed in the register of members' interests later that year.

The timing was thrown into focus on Tuesday when James Murdoch revealed this was the moment his company was weighing up whether it could overcome the likely obstacles to a takeover bid for the share of Sky it did not already own.

James Murdoch told the Leveson inquiry: "I remember there was a meeting in the summertime about it in Los in sort of August, Angeles, but that was sort of where it was coming – starting to come together, thinking: would it be possible to do that?"

Critics of the bid are questioning whether this could be the moment News Corp was given the political green light.

On 30 August, Hunt, then the Tories' culture spokesman, left for New York. He declares on his register of interests that he funded the trip with £4,000 taken from donations to his office by a regular supporter, John Lewis, a wealthy lawyer and businessman. The donations paid for flights for two and accommodation.

Hunt did not reveal who he saw at News Corp's headquarters. His register entry says: "Purpose of visit: to look into local media ventures. Meetings with representatives of News Corp (including Wall Street Journal), Fox Five and WNET."

Hunt returned from the US on 4 September 2009. Six days later, James Murdoch, who was in charge of the as-yet-unannounced Sky bid, met Cameron, then leader of the opposition, at the discreet George Club in Mayfair, and gave him the news that the Sun would switch its support to the Conservatives.

Labour politicians, who are calling for Hunt's resignation over his secret links with Murdoch during the bid process, are likely to see the timing of his 2009 visit to News Corp as more evidence of a link between the Sky bid and the Sun's switch of political allegiance. They want Hunt to say whether he discussed the Sky bid or the likelihood of Tory support for it during his visit.

The Labour MP Tom Watson, a member of the culture, media and sport select committee, said Hunt's journey to the US was suspicious: "After the James Murdoch revelations, this points the finger of suspicion at this particular trip.

"What was discussed, who did Jeremy Hunt meet?

"If the possibility of the BSkyB bid was discussed at any point, did Mr Hunt declare this to MPs in the chamber? Who did he go with? Leveson will see this as a disastrous piece of timing and the inquiry is allowing people to join the dots about the web of connections spun by Rupert Murdoch's News International."

At the same time as Hunt's trip to visit News Corp in the US there was a flurry of activity. James Murdoch used his MacTaggart lecture on 28 August in the UK to publicise a set of demands that were in the commercial interests of News Corp's UK broadcasting interests.

Without disclosing that News Corp was planning after the election to launch a bid to take over the whole of BSkyB, he called for the power of media regulators to be reduced. He said: "A radical reorientation of the regulatory approach is necessary if dynamism and innovation is going to be central to the UK media industry. Intervention should only happen on the evidence of actual and serious harm to the interests of consumers: not merely because a regulator armed with a set of prejudices and a spreadsheet believes that a bit of tinkering here and there could make the world a better place."

He added that the BBC was "dumping free, state-sponsored news on the market". The next day he called for the licence fee to be cut and the BBC made "much, much smaller".

And in what appeared to be a deliberate piece of timing to inflict maximum damage on the then Labour prime minister, Gordon Brown, the announcement of the Sun's switch to back the Tories was delayed until 30 September, when Brown was due to address his party conference. Rupert Murdoch apparently had breakfast with Cameron that morning, according to the News Corp evidence submitted to Leveson, and he would have been able to see the Murdochs' handiwork on that day's Sun front page. Rupert Murdoch disputed this at Leveson on Wednesday, saying: "I wasn't here on the day we came out for the Tories."

A spokesman for Hunt's department declined to answer questions, saying: "He made a statement yesterday and we're not adding to it. We're not commenting." Asked if he was prepared to take questions, the spokesman said: "No, we're not adding to the statement."

REGISTER ENTRYJeremy Hunt's US trip in the register of interests

• Name of donor: John Lewis

• Address of donor: private

• Amount of donation (or estimate of the probable value): £4086.47 (flights and accommodation for two people). The money came from a donation that has already been declared – see Category 4 above.

• Destination of visit: New York, USA.

• Date of visit: 30 August to 4 September 2009

• Purpose of visit: to look into local media ventures. Meetings with representatives of News Corp (including Wall Street Journal), Fox Five and WNET.

(Registered 27 November 2009)