The size of these bricks is exactly 3x the regular system.
Not much is known about these European bricks yet. As far as I know (but I might be misinformed) they were released in sets 501 (1966-1968), 502 and 503 (1968) in the United Kingdom only, but these bricks can be found in Denmark also.
I am calling this the “European” version by lack of a better description, even though the British production might mean that these bricks could have been sold in Australia also.
[Original post and comments on Flickr.]