Rupert Murdoch's recurring dream of owning Britain's biggest pay TV provider won't become reality until at least 2018.

A planned $15 billion takeover of Sky by 21st Century Fox (FOX) faces many more months of scrutiny by U.K. officials after Murdoch declined to offer new concessions to protect Sky's editorial independence, according to sources familiar with the matter.

U.K. culture secretary Karen Bradley said last month that she would order an additional review of the deal unless Fox were able to assuage concerns that it would give the Murdoch family too much influence over British media. The deadline for Fox to submit new proposals is midday ET on Friday.

Spokespeople for Fox and the British government declined to comment.

The additional review would be conducted by Britain's Competition and Markets Authority.

Fox said last month that it expected an investigation by the CMA to take at least 24 weeks and prevent the transaction from closing before June 30, 2018.

It would have to pay Sky £200 million as a break fee if the deal falls apart.

Sky (SKYAY) shares slipped 0.7% in London to trade at £9.68, nearly 10% below Fox's offer price of £10.75.

Related: Setback for Murdoch's $15 billion Sky deal

Bradley has said the proposed company would have the third largest reach of any news provider in the U.K., uniquely spanning television, radio, newspapers and digital publications.

The question is whether the deal would increase Murdoch's influence over British politics and public opinion. He already controls three major newspapers -- The Sun, The Times and The Sunday Times.

Bradley rejected initial proposals from Fox and Sky aimed at addressing those concerns -- including establishing an editorial board for Sky News with a majority of independent members. The board would oversee the appointment of the head of Sky News.

The companies had also offered to maintain Sky-branded news for five years with no reduction in its budget.

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This is Murdoch's second attempt to buy Sky. A previous bid collapsed in 2012 in the wake of a phone-hacking scandal at his British newspapers.

Sky (SKYAY) has 22 million customers in five European markets: Italy, Germany, Austria, the U.K. and Ireland.