Ofcom and the Competition and Markets Authority are to examine 21st Century Fox's proposed £11.7 billion takeover of Sky, the Government has announced.
Culture Secretary Karen Bradley told MPs she has issued a European intervention notice on the grounds of "media plurality and commitment to broadcasting standards" linked to the bid from Rupert Murdoch's company.
Ms Bradley confirmed the decision in a statement to MPs in the Commons.
Ms Bradley told MPs that she had considered representations from the broadcasters but she was not satisfied that her concerns had been addressed.
She said: "While the representations from 21st Century Fox highlighted areas where it contested the position taken in my minded-to letter, none of the representations have led me to dismiss the concerns I have regarding the two public interest grounds I previously specified.
"I am of the view that it remains both important, given the issues raised, and wholly appropriate for me to seek comprehensive advice from Ofcom on these public interest considerations and from the Competition and Markets Authority (CMA) on jurisdiction issues."
Ofcom and the CMA will have until May 16 to investigate, she said.
Ms Bradley said the regulator Ofcom would also conduct a "fit and proper" test into the corporate governance at the same time, after concerns were raised by MPs about the running of Murdoch's media empire.
She said: "On Monday Ofcom announced that it will conduct its fit and proper assessment at the same time it would consider any public interest test in response to my decision to intervene in the merger.
"This means Ofcom will conduct its assessment within the 40 working days it has to report to me on the public interests I have specified in the intervention notice.
"I welcome Ofcom's announcement - which will provide clarity for the parties but also provide reassurance to those who have expressed their own concerns about this issue - that this is a matter which Ofcom will now consider before the merger takes place."
Shadow culture secretary Tom Watson welcomed the move and urged 21st Century Fox not to frustrate the investigation.
He told Ms Bradley: "You will have noticed that 21st Century Fox is happy too. In a letter to you last week they said, and I quote, 'that we welcome a thorough and thoughtful review'.
"I have no doubt that welcome is sincere and 21st Century Fox are thrilled by your decision.
"I hope that on that basis they will seek not to challenge it, or to impede any element of Ofcom's investigation.
"If they do, I trust that you will make a new referral to put it beyond doubt that Ofcom will investigate what it needs to."
A 21st Century Fox spokesperson said it was keen to co-operate with the investigation and it was confident that the merger will be approved.
The spokesperson said: "We are confident that a thorough review of our track record over 30 years will underscore our commitment to upholding high broadcast standards, and will demonstrate that the transaction will not result in there being insufficient plurality in the UK.
"The media market has changed dramatically in recent years, as has our business.
"We believe our proposed £11.7 billion investment will benefit the UK's creative industries.
"We look forward to continuing to work with all stakeholders and are confident that the transaction will be approved."
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