Why is the pound so strong and worth so much against other currencies?

A Question i pose to all you out there:

Why is the UK pound worth so much compared to all other currencies? Its a qn that hasn't answered been well ... surprisingly its fallen in value over the years & back in the 1940's 1 Pound = $4 USd can u believe it!! The UK now imports much produce & goods, there is less manufacturing, more imports & less exports. It is become a booming sector for banking & finance but thats not enough to explain it all. anyone know?