Multiple currencies for Credit cards

[Tom Haskins-Vaughan]

I have credit cards in GBP and USD. Do I need two separate expense 
accounts as follows:

Expenses:Banking charges:Credit Card Interest USD
Expenses:Banking charges:Credit Card Interest GBP

Or would one do?

I'm thinking that if I only had one, then the exchange rate would come 
into play for each monthly fee.

Liabilites:US Credit Card -> Expenses:Banking charges:Credit Card Interest

Whereas if I had two separate expense accounts then the exchange rate 
would only be important when I was compiling reports, e.g. a balance sheet.

What are people's thoughts?

Tom