term length varies, but 10 lessons per term is not one per week, its less than one per week.
Xmas term from sept. to dec. is usuall 14 weeks ( not including the 1 week half term) the other 2 terms vary upon dates of easter, but are usually 12 weeks and 13 weeks respectively ( easter and summer term, again not including the half term break) giving the total of 39 weeks that is a school year in most counties in the UK
hope that helps