I need to go to the toilet

So - in America people don't say toilet. This place is the restroom or less formally the bathroom. But in London - its the loo or the toilet.
I was in Marks and Spencer the other day and I asked a sales assistant where the rest room was. She looked at me in a strange way. And my cousin nudged me and said - say the toilet. Oh yeah.
Its funny because we don't say toilet in America and I'm sure if I asked someone where the toilet was - they might turn an embarassing shade of red!!!