United Nations Security Council (UNSC) is the last, most exclusive club in international relations. Reforms of the UNSC need to be negotiated on a written document instead of holding verbal promises.
Superficial Declarations
No support from P-5: Although the permanent members do make some noise about supporting a new entrant, the fact is that none of the five permanent (P-5) members wants to see UNSC ranks to be increased. Intrinsically each of them is confident enough that the idea of its enlargement will shoot down by one among the P-5.
Intricacies of membership
Unhappiness about the right to veto: P-5 are no saints. The members of the P-5 club have used this privileged right on many occasions in a biased manner. For example, western members use the veto to protect Israel when the Palestinian question was being discussed; Russia, in its incarnations as the Soviet Union and the Russian Federation, has cast more vetoes than its western counterparts.
Support and Opposition: India, Japan, Brazil, and Germany are the declared candidates for permanent membership, called G-4. Pakistan and China will oppose India; China also doesn’t support Japan; Brazil has regional opponents and claimants; Italy is firmly opposed to Germany’s claim.
Amending the charter: Changing the membership of the Council requires amending the Charter. This involves the consent of two-thirds of the total membership of the U N, including the concurring votes of P-5. This means that each of the five has a veto.