Never mind light relief, the chapters in this book are absolutely bite-sized. There is nothing new in dumbing down - Sellar and Yeatman were well practised in this art in 1930. The style is schoolboy humour throughout - indeed, it was very little surprise to read that much of the material originated in the pages of 'that other mildly satirical magazine', as Private Eye often described it.
At the highest level, it's a galop through English history from the Roman invasion to the Great War. At almost every turn the authors manage to mangle names, facts, theories, or all three. It is all those e-mails you've ever had about the "amusing" things children write in their exam papers.
Though as an aside, I should point out that I did have a summer job for two years checking the adding up on A-level papers. A number of students did write essays about the great economist Milton Keynes.