England's record-breaking rugby win over New Zealand's Black Ferns was achieved in part using underhand tactics at North Harbour Stadium.

The Black Ferns' 10-year unbeaten run was dashed by their 17-22 loss to England on Saturday.

But the English management team had an unexpected helping hand as they stumbled on the radio frequency that the New Zealand coach, Darryl Suasua, and his assistants were using to field calls from the grandstand to the sideline, and tuned in for the entire match.

Suasua only found out that England were eavesdropping on the New Zealand tactical conversations at the after-match function when the English physiotherapist confessed to former New Zealand captain - and now team physio - Helen Littleworth.

"They knew what we were doing the whole match," Suasua said. "They heard my calls about where the holes in their defence were. I wondered why those gaps suddenly closed. It was a kick in the guts. The girls sweated their brains out there. They gave their all and I feel we lost it for them off the field."

The winning try by Emily Feltham was brought into question, the English well aware that the New Zealand side were worn out, courtesy of Suasua's information he thought he was telling just his staff.

New Zealand were leading 17-15 going into the final minutes, but were wilting after a physical opening hour. Then Suasua made the comment via his headset.

"I said, 'We've lost our spark, we have to dig deep,' and on hearing that, England offcials said after the game that that was when they went for it.

"They started to throw absolutely everything at us," Suasua said.

He is sure that without the inside knowledge England would not have realised New Zealand were tiring rapidly.

While the loss reduced some of the team to tears, Suasua is pleased that they were beaten now rather than at next year's World Cup in Spain.

"I said to the girls, take a big, long whiff of that because that's what defeat smells like."