June 30 (Reuters) - Britain's competition regulator said

on Monday it has begun a Phase 1 investigation into planemaker

Boeing's ( BA ) deal to acquire Spirit Aerosystems ( SPR ) and

set a deadline of August 28 for a decision.

The Competition and Markets Authority (CMA) had said last

week that it was weighing a probe into whether the deal could

affect competition in the country or in other markets.