The review, led by Treasury Chief Secretary Danny Alexander, said there are alternatives to the UK's current nuclear stance which requires at least one nuclear-armed submarine always to be at a sea.
However, it accepts that cutting the size of the current four-vessel fleet would not offer the same degree of resilience as the current continuous-at-sea deterrent and would not guarantee "a prompt response in all circumstances".
More top news
The EgyptAir plane that crashed into the Mediterranean Sea did not swerve before disappearing off radar, according to Egyptian authorities.
Jose Mourinho is a step closer to being appointed the new Manchester United manager after Louis Van Gaal's turbulent reign was ended.
Greek authorities began to clear the country's largest informal refugee camp on Tuesday - blocking access to the area in the process.