Incorrect currency showing until customers load the product

Hi, I’ve got a UK based site with multi currency installed. I’ve got UK customers who say that when they visit my site it shows the items in australian dollars, canadian dollars or US dollars to start with and only when they click on a product to view it does it change to GBP. I’ve had the auto currency switched but GBP is the default currency otherwise so I don’t know why it’s showing the incorrect currency.

Then I turned off the auto select hoping that would be a temporary fix and I set it to default GBP but it’s still loading for some people as US dollars. How can I fix this?