The British government can show world leadership if the UK ambassador to the United Nations makes a proposal to a) remove Russia from the security council and b) invite Ukraine to be the legitimate inheritor of the position of the Soviet Union as described and allowed in the United Nations Charter.
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The 1949 UN Charter stated “The Republic of China [RoC], France, the Union of Soviet Socialist Republics, the [UK], and the [USA] shall be permanent members of the Security Council.” Two of those countries have been replaced. The Russian Federation is NOT the USSR. As part of the former USSR Ukraine has as much right to replace the old USSR as Russia.
A precedent to remove a member of the security council happened in 1971. The UN General Assembly removed Taiwan [RoC] from the security council.