Form is not secure

Hi,

I have started to get the following message when I click to add an item to the shopping basket -

"The information you’re about to submit is not secure
Because this form is being submitted using a connection that’s not secure, your information will be visible to others"

This hasn't happened before and I was wondering if there is something I need to do to make it secure? The checkout page is ok so I think it is just when adding something to the basket.

Thanks
Kate

Thank you!