The provision is there to maintain future flexibility, so that there is no need to revisit the primary legislation if circumstances dictated that we needed a separate trading scheme.Clearly, there could be advantages in having a separate scheme in certain conditions, but equally there could be disadvantages, because a smaller market for trading might have a bigger range of buying and selling prices. At this stage, it is not clear what the balance will be.We also have to take account of what Europe might end up doing with emissions trading.