Whatever currency we use, it is the world markets that dictate its strength and in turn how well our economy is fairing.
If we did have control over sterling and if this did mean we had full financial control of our economy, why is the pound dropping so rapidly? The truth is, there is no control.
As long as we are tied to a strong currency, it does not matter what it is. There are quite a few places outside the United States that use the US dollar or peg their local currencies to the US dollar. That does not mean they lose control of their own economies.
Question Time audiences are scrupulously chosen to be equally representative of the political spectrum. The fact that the Tories in the audience had little to say about World finances and the Economy might be due to the fact that their party does not have a policy other than gawp from the sidelines and scratch its head in bewilderment.