How did the Tories not see the school concrete crisis coming?

Parliament is back from recess and the row which will be dominating MPs inboxes is the school concrete crisis, which has disrupted the start of term for over 100 schools. Why didn't the government act sooner? 
 
 James Heale speaks to Katy Balls and Isabel Hardman. 
 
 Produced by Oscar Edmondson.