why is it not permissible in Islam for women to shake hands with a man?

A British man came to a Muslim and asked :
why is it not permissible in Islam for women to shake hands with a man?
The Muslim said: Can you shake hands with Queen Elizabeth?
British man said : Of course not, there are only certain people who can shake hands with Queen Elizabeth .
Muslim replied: Our womenare our queens and queensdo not shake hands with strange men ..!