Microsoft’s planned $100 billion purchase of Activision Blizzard has been blocked by the UK’s antitrust watchdog, effectively killing off what would have been the biggest gaming deal in history.

The Competition and Markets Authority said none of the proposed remedies, including Microsoft’s deals with competitors to allow Activision’s flagship title Call Of Duty onto rival gaming systems, are sufficient.

Microsoft and Activision have vowed to oppose the decision, but the UK block, followed by the US Federal Trade Commission suing to block the merger in December, means the takeover is all but dead in the water.

Credit: Call of Duty

The merger agreement expires on July 18, after which Activision can exit from the deal with A$4.5 billion.

Activision shares dropped 11.45 per cent after the merger was blocked, forcing the company to release its rosy first-quarter financials a day earlier, in an attempt to stem the bleed.

Revenue for the quarter came in at $3.6 billion, beating estimates of $2.68, while net income almost doubled, jumping from A$597 million to A$1.12 billion.

The company said monthly active users were 368 million during the quarter.

“We remain confident that our deal with Microsoft benefits competition, consumers and job creation in markets around the world, especially in the UK,” Activision CEO Bobby Kotick said of the decision to appeal.