I think he knows him from the school. The Prime Minister bullied him.

They were schoolmates

Yeah they were schoolmates.

Yeah they were shool mates

Prime minister bullied sayle

Mr Sayle and the Prime Minister were at school together. In Stormbreaker, Sayle says that the Prime Minister was a politician even back then and that he was a nice kid in front of the teachers and in their absence bullied Sayle. The Stormbreakers were supposed to be a revenge against the British as Mr Sayle thought that all Britishers looked down on others.

Yeah they were schoolmates. tbf the plot of the first four novels were kind of childish, with the plot being some guy wanting to rid the world or some part of it. Things really get interesting when we learn about SCORPIA, and it turns out, SCORPIA was the one who supplied the virus to Herod Sayle in the first place.