The veto is a way of keeping national sovereignty over sensitive areas of decision-making.

The veto can be used when ministers from the national governments vote in the Council of Ministers on a number of issues, including defence, taxation and social security.

But with another 12 countries poised to join the EU, the veto could potentially make it even more difficult for the Council of Ministers ever to reach a decision.

For this reason, the Treaty of Nice, negotiated in December 2000, extends the council's other decision-making process - qualified majority voting - into a number of new areas and so removes the national veto.

In the future, individual member states will no longer be able to veto decisions on the distribution of funds to help poorer regions, some parts of visa, asylum and immigration policy and some trade agreements.

The veto will also be lifted on closer co-operation, which allows groups of countries to forge ahead on certain issues without involving all the member states.