Just had my "summary" for 2015-16, this is the slick one page glossy which includes a pie chart of contributions to public spending.
They've got all the basic figures right (income, basic and higher rate tax) but the *total* income tax figure is just added up wrong.
They conclude that I pay 20% of my taxable income in tax (on their numbers it is 23%), while the figure is actually just over 30%.
On the whole, I suppose they are trying. I would hate to be the person who was signed off the verification of the code doing that calc, though!