David Cameron has said that Britain's best future is the EU, providing member states can get proposed reforms right.
Speaking at the end of a two-day EU summit in Brussels, the PM said Britain's leading role in an "unstable world" on issues of security highlights the importance of the ongoing renegotiation. Mr Cameron had been speaking about the UK's role in global security and the fight agaist the self-proclaimed Islamic State - also referred to as Daesh.
In an unstable world, Britain is playing a leading role in the EU on issues of security, working with other member states so we better protect our people...
... I believe if we can get these reforms right - and I believe that we can - I firmly believe that for our economic security and increasingly for our national security, the best future for Britain is in a reformed European Union.
Poland could drop fierce opposition on plans to cut EU benefits in return for a deal on new NATO bases, the country's foreign minister said.
Britain leaving the EU risks leading to the break-up of the UK, while "gravely weakening" the continent's security, William Hague warned.
The fact is if Britain leaves the EU a new relationship would have to be forged - we've no idea what that relationship would look like.