Completed - boom!! Was harder and I got a stitch during my last 90 second run but ran through it and a man feeling rather proud. In particular as I am a master of procrastination and managed to reduce this to only thinking about it for half an hour before convincing myself to just get on and do it.
Also, changed my trainer to Sarah millican. She doesn't talk as much as jo but I didn't suffer any set backs with the countdown stopping mid run. Thanks Sarah!