David Cameron visited Rupert Murdoch's Wapping headquarters in London on Monday night to address a closed-doors conference, just days before his government is expected to give regulatory approval to the controversial £8bn takeover of BSkyB by the media mogul's News Corporation.

With Murdoch himself present, Cameron gave an early-evening keynote speech to a "CEO summit" organised by the Times – although the event programme published on the newspaper's website coyly described him as an unnamed "senior cabinet minister".

The programme indicated Cameron would also be taking questions from those present – a mixture of senior business executives and News Corp and Times staff. But the prime minister did not attend the summit dinner immediately after his talk, avoiding more informal contact with Murdoch and senior executives.

Outside journalists were not invited to the Times summit, which runs on into Tuesday with an early-morning speech from Ed Miliband to provide political balance, followed by a mid-morning interview with Rupert Murdoch conducted by News Corp employee James Harding, editor of the Times. Murdoch will be discussing "the next digital revolution".

A ministerial decision on whether to approve News Corporation's bid for BSkyB has been expected for several days and could come this week. The decision is taken by Jeremy Hunt, the culture secretary, who acts in isolation.

Hunt has previously indicated he is minded to approve the merger on condition that News Corporation agrees to spin off Sky News and restrict its shareholding in the channel to 39.1%.

A string of media organisations, including the parent company of the Guardian, have opposed the proposed Murdoch merger, arguing it would stifle media plurality by bringing together the largest newspaper group, Sun and Times owner News International with a 37% share of all copies sold in the UK, and the largest broadcaster, BSkyB.

Last year the fast-growing Sky had a turnover of £5.9bn, taking it comfortably ahead of the BBC.

Last Thursday Cameron turned up at Murdoch's annual summer party in Kensington Gardens, London – an event also attended by Ed Miliband but not by Lib Dem leader Nick Clegg or by Hunt. Tom Watson, Labour MP for West Bromwich East, said: "This will be the second time in a week that David Cameron will have moved around his schedule to be with Rupert Murdoch, at a time when the announcement of the Sky decision is imminent. I hope the two facts are not related.

"There is now a cross-party resolution asking for a public inquiry into the News of the World phone hacking affair. I also hope that the prime minister will have the courage to address the hacking issue with Mr Murdoch directly."

The delay in publishing a final approval for the takeover is due to intense negotiations on points of detail of the Sky News spin-off agreement between News Corporation and regulators Ofcom and the OFT, who are both advising Jeremy Hunt.

Regulatory sources say they want to structure the legal agreement "so it cannot be got around" – an attempt to head off a perception that Rupert Murdoch has been successfully able to work around previous legal agreements he has signed designed to secure the editor's independence at the point when The Times was acquired in 1981 and when the Wall Street Journal was bought in 2007.

In both cases the agreements were designed to prevent the editor of both newspapers from easily being removed, but in practice editors at each title have come and gone largely at the behest of the owner.

Hunt is expected to announce that the deal will go through shortly after he receives final reports from Ofcom and the OFT, but these have yet to reach his desk.

The long delay has frustrated Murdoch's News Corp, which is keen to conclude the transaction at a time when BSkyB's share price has been rising due to its strong financial performance.

News Corp's original proposal was made at 700p a share a year ago, but Sky's share price was 830p yesterday. A final bid is thought likely to succeed at around 875p – costing News Corp about £1.8bn more than the original £7.5bn proposal.