Britain's competition regulator said on Wednesday it had launched a formal investigation into Amazon.com Inc's investment in food delivery company Deliveroo, setting a December 11 deadline for a decision on the first phase of its probe.

The Competition and Markets Authority (CMA) said it was looking into whether Amazon's investment in May, when it led a $575 million fundraising, could result in a "substantial lessening of competition" within the United Kingdom.

Deliveroo, a British online food delivery company, was Amazon's inroad to pit itself against Uber Eats in the race to dominate the market for takeaway meals, worth around $100 billion globally.

The CMA previously ordered Amazon and Deliveroo to operate independently on concerns that the companies had "ceased to be distinct" or were putting in place arrangements which would result in the same.

However, Amazon said its investment will allow Deliveroo to expand its services and create new jobs.

Amazon declined to comment, while Deliveroo did not immediately respond to Reuters request for comment on the CMA's probe announcement.

(Reporting by Uday Sampath in Bengaluru; Editing by Bernard Orr and Shailesh Kuber) ((UdaySampath.Kumar@thomsonreuters.com; within U.S.+1 646 223 8780; Twitter: @sampath_uday; Reuters Messaging: UdaySampath.Kumar.thomsonreuters.com@reuters.net))