"I attended a drowning in the same place two years ago, and, being a local and aware of the real dangers associated with swimming on this part of Ninety Mile Beach, I deemed it serious enough to offer assistance," he said.
His son, until very recently a St John cadet in Kaitaia, was keen to help.
"He is an accomplished and qualified first aider, so I knew he would be a real asset to me," he said.
"The sea was very rough, with 2m waves breaking more than 100m out. When the conditions are rough, this area is notorious as being a dangerous place to swim.
There is a hole and a severe tidal rip that has taken the lives of others."
Two women who were among bystanders on the beach told him two people were in the water and needed saving, although he could only see one, about 100m off the beach.
Advised by police communications the fire brigade was still 25 minutes away, and a rescue helicopter 35 minutes, he decided to go into the water. He told communications there would certainly be a drowning if he had to wait for the emergency services.
"I had assessed the risk, and made a calculated decision to attempt a rescue," he said.
"I am an accomplished swimmer - I was a surf lifesaver in my early teenage years. I've swum competitively and played water polo - and, although the sea was treacherous, I believed I had a chance of being successful."
First attempt
Paul Desmond, owner of the nearby backpackers' accommodation (where the woman who died was a guest), had also attempted a rescue but had returned to the beach exhausted and in fear of his own safety. Mr Critchley borrowed his life jacket and surfboard and entered the water.
"The sea was a mass of foam," he said.
"I was getting smashed. The waves kept forcing me back.
"I remember looking back to shore and being guided to the exact location of the male I was trying to rescue. I still couldn't see a second person."
He finally reached man he had seen from the beach, exhausted and distressed, who had successfully rescued one woman.
He had returned to the water, with no flotation aids, in a bid to save the woman who died. Police yesterday named her as 23-year-old Carolin Klara Emma Jentsch of Germany.
Two more women got back to the beach unassisted.
Mr Critchley got the struggling man on to the surfboard and returned him to the beach, then went out again, and found a young woman, face down.
He tried to resuscitate her with "a couple of quick breaths," but she was unconscious.
Read more:
• Woman drowns at Ninety Mile Beach
"I tried to prop her head out of the water on the board as I swam hard for shore.
"The surf kept crashing over us, and I had to keep making sure her head was out of the water.
"I don't have a real concept of time at this point, but it felt like 10 minutes before I finally made it to shallower water, and I again gave her two breaths."
A fire brigade crew that had arrived by that time began CPR, while an exhausted Mr Critchley was treated by a St John crew.
The man he had saved later told him that he had reached the woman who died, but a wave had crashed over him and he had lost his grip on her.
He had tried to breathe into her mouth but he was spent.
She had been face down, and he believed she had died before he reached her.
This was not the first time that Mr Critchley had risked his life for others.
In 1991, shortly after he joined the police force in his native England, he went into the Ribble River in Lancashire in an unsuccessful attempt to save a 14-year-old boy.
He was able to retrieve the teenager's body.
"It turned out quite some time later that it was a homicide," he said.
A man who was at the scene was eventually found to have pushed the boy into the water.
Mr Critchley's heroism was recognised with the Liverpool Shipwreck Society Award.
