U.S. cybersecurity firm NortonLifeLock Inc's $8.6 billion purchase of rival Avast Plc will face an in-depth probe by Britain if competition concerns are not addressed, the UK anti-trust regulator said on Wednesday.

The Competition and Markets Authority (CMA) said the deal could lead to British customers getting a worse deal when looking for cyber security software.

"We are living more of our lives online and it is vital that people have access to competitive cyber safety software when seeking to protect themselves and their families," CMA Executive Director David Stewart said in a statement.

The two cybersecurity companies need to submit proposals to allay the regulator's concerns within five working days, after which the CMA will review their proposals and decide whether to take its investigation into phase 2.

Avast and NortonLifeLock did not immediately respond to a request for comment.

The CMA started its initial probe in January into the cash-and-stock deal, which was announced in August and aims to create a leader in consumer security software.

  - Reuters