No need to go to any links as its all printed on the bottom left hand corner of your (uk) medical certificate.
"Class 1 single pilot air transport operations carrying passengers", under 40- valid 12 months, 40 plus-valid 6 months.
"Class 1 other commercial operations" (i.e. multi crew, aerial work etc.) under 60-valid 12 months, 60 plus- valid 6 months.
It also shows the validity against age for class 2 and ECGs etc.