* UK government intends to submit deal to in-depth probe
* UK concerned about Murdoch's influence over news agenda
* Sky would remain 'fit and proper' under Fox ownership
* Takeover could now complete only next June (Adds reaction)
LONDON, June 29 (Reuters) - Britain intends to subject Rupert Murdoch's takeover of European pay-TV group Sky to a lengthy in-depth investigation after finding the $15 billion deal risks giving the media mogul too much power over the news agenda.
Media Secretary Karen Bradley said she was persuaded that Twenty-First Century Fox's bid could give the Murdoch family excessive influence over the media, after regulator Ofcom assessed the impact of the deal.
"The proposed entity would have the third largest total reach of any news provider - lower only than the BBC and ITN - and would, uniquely, span news coverage on television, radio, in newspapers and online," Bradley said.
The Media Secretary said she would take a final decision on July 14, giving Fox two weeks to address her concerns. Shares in Sky rose on hopes a full investigation could still be averted by concessions over its 24-hour TV news channel.
Murdoch, 86, and his family have long coveted full control of Sky, despite the damaging failure of a previous attempt in 2011 when their British newspaper business became embroiled in a phone-hacking scandal which forced them to abandon that bid.
A public inquiry into the affair revealed deep ties between Murdoch and the political establishment, making the renewed bid potentially toxic for Prime Minister Theresa May's government which is fighting for survival after losing its majority.
Bradley had asked regulators to examine whether Fox would have too much control of the media, and whether it would be committed to upholding broadcasting standards if allowed to buy the company which broadcasts in Britain, Ireland, Germany, Austria and Italy.
Fox said it was disappointed by the government's rejection of its plans to maintain editorial independence of Sky News, and said a full investigation could push the deal's completion date back to next June. "We will continue to work constructively with the UK authorities," it said.
During the previous takeover attempt Murdoch proposed spinning off Sky News into a separate company. However, Ofcom said on Thursday it was concerned that separating Sky News could be counter-productive, given the potential difficulties in funding the service outside of the Sky structure.
"FIT AND PROPER"
The British government said on Thursday Ofcom had no concerns about Fox's genuine commitment to broadcasting standards but wanted to look further into the impact a deal would have on the range of media providers in the country.
Britain's political leaders have long sought the backing of Murdoch and his Times and Sun newspapers, sparking accusations that he uses his media empire to play puppet master in the corridors of power.
Tom Watson, deputy leader of the opposition Labour Party and a long-standing Murdoch critic, said the government was going through the motions and would ultimately approve the deal.
"The parties will offer up something new, which they always had in their back pockets, the secretary of state will accept them, as she always planned, and this merger will go ahead," he said.
History shows, he said, that any concession by the Murdochs would not be "worth the newsprint" it was published on.
Ofcom also carried out a separate investigation as to whether a Fox-controlled Sky would be a 'fit and proper' owner of broadcast licences in Britain.
The regulator said allegations of sexual and racial harassment at Fox News in the U.S. were extremely serious and disturbing but had found no clear evidence to suggest senior executives at Fox were aware of the misconduct.
Fox tried to pre-empt government concerns over the impact on Sky's editorial independence by proposing the creation of an independent board to run Sky News, the company's influential 24-hour news channel.
But Bradley said she was minded to reject the proposal after Ofcom suggested that the undertakings were not strong enough.
"Sky will continue to engage with the process as the Secretary of State reaches her final decision," the company said in a statement.
Launched in 1989, Sky used exclusive Premier League soccer to draw in customers to pay-TV and pioneered round-the-clock news to make it a major player politically and commercially.
It now broadcasts to 22 million homes, competing with the publicly-owned BBC and ITN, commercial TV's news provider.
The latest delay to the deal will come as a blow to the Murdoch family after they split their newspapers from television and film assets into two separate companies, even though they retained a grip on both due to their ultimate ownership.
Rupert's son James, who is chief executive of Fox and is currently chairman of Sky, said in March that worries about his family exerting too much power were unfounded in an era of online providers such as Facebook, Buzzfeed, Netflix and Google.
Shares in Sky have been trading at a discount to the 10.75 pounds offer, indicating that although investors were not expecting outright rejection, there was still some concern about any undertakings required from Fox to get the deal through.
The stock was trading up 3 percent at 987 pence on Thursday afternoon in the belief that Fox would find a resolution. Analysts at Citi said Fox could even find a resolution before the July 14 deadline and avoid the lengthy referral.
"Ultimately this is a positive outcome for the Fox/Sky in the sense that it makes deal completion more likely," they said.
"Concerns about broadcasting standards would have been almost impossible to work around while we believe the groups will be able to offer concessions that adequately address concerns about plurality."
(Editing by Guy Faulconbridge/Keith Weir)