Yes that's it.
I could make it manually but it would be such a chore to work out all the holidays for the U.K etc. I saw that calendarlabs site but the resolution of their templates were low I believe - difficult to scale to A1.
There is a plugin for InDesign called Calendar Wizard which is really good, but it doesn't have the U.K hols file and it doesn't to the horizontal months, It generates the calendar like the image you posted.
Really appreciate you help, mish.