There are five permanent members on the UN Security Council, they are UK, USA, China, France and the Russian Federation.(1)
THE CASE FOR A #FREEBRITAIN
"It is enshrined in the Charter of the United Nations that the United Kingdom is a permanent member of the United Nations Security Council. Removing the UK from the Security Council would be an unprecedented step, most likely an amendment to the charter, requiring the support of two thirds of members of the UN General Assembly.
If we remain in the EU, however, the Union may eventually be able to persuade enough countries that since the UK is part of the EU, and subject to the EU Common Security and Defence Policy (CSDP), that Brussels should be able to control the UK's veto and vote at the Security Council."
Steven Woolfe MEP