The site mentions that there are exactly 50 blocks to the square meter,ie 200mmx100mm,dose that include the gaps between blocks ie the blocks are slightly less than as stated to allow for the spaces,thaks for your help I am a complete novice.
What you want to be careful of is trying to say 100 blocks laid as soldiers will fit a gap of exactly 10m. There is always a bit of give and take. Tony has done a good page on the actual spec of pavers. It does allow for some differences in individual block sizes.