I went to my big Asda in Castleford yesterday and saw that Vileda Super Mop replacement heads were £3.67 or 2 for £3.00. The shelves had all the decor marked up so I am sure its not store specific, not online by the looks of it though.
I have searched to see if it has already been posted and couldn't find it so hopefully not a duplicate deal
Hope this helps someone. :)