The DIY SOS star ripped open a door of the Ford Mondeo and rescued Claire Williams, 28, and baby Alexandra with the help of another motorist.
'The car span out of control, flipped three times or four times and landed on its roof,' says Claire.
'I was knocked unconscious. When I woke up Nick reassured me and told me I was in safe hands. He was a hero.'
But Nick, 47, has played down his actions following the accident near Taunton, Somerset.
'I just did what everyone else would do,' he tells the BBC.
'I would hope anyone else would have done the same to help my loved ones.'
Claire escaped with minor injuries while the baby was saved by her child seat.