Both of these expressions exist in British English. They do, however, have different meanings and are commonly mixed up, even by large British supermarket chains on their in-store signs!
This is used to mean that something is happening daily, as in the following examples:
* We do this every day.
* Every day, we like to contact Future Perfect.
* Available all day every day.
This is an adjective (or describing word) meaning ‘ordinary/regular’, as in the following examples:
* This is an everyday occurrence.
* It’s just an everyday event.
* It’s an everyday object.
The bottom line:
Everyday is a single word and is an adjective, so it's the one that is used in front of a noun to describe something as normal or commonplace.
Every day is an adjective (every) plus a noun (day), and it means each day.