IIRC the mandatory stress test (mandated by FinReg) for mortgage affordability is a rate rise of 2% (not 1% Pete).
Not only was this probably not high enough, but its accuracy is also questionable given the economy with the truth that people tend to fill in on their outgoings ("forgetting" to mention personal loans and other commitments which impact monthly affordability significantly). As Macy said above, brokers and banks in many cases encouraged applicants minimise their outgoings in order to get a larged approved amount.