"I think it's a place that's mastered to art of being on high alert while they go around their daily life. If this turns out to be a calculated terrorist attack of course that would have an impact on people's level on alertness in London."
A Ministry of Foreign Affairs and Trade spokeswoman confirmed the Prime Minister's understanding was correct.
"The New Zealand High Commission in London is providing consular assistance to the family of a New Zealander injured in the incident at Parsons Green underground station," she said.
Due to privacy considerations, the Ministry would not provide further comment.
English ruled out increasing New Zealand security levels.
"No, no, we have seen nothing like that," he said.
Several people were injured in the incident on the packed underground.
People fled in panic after a "fireball" reportedly left several passengers with facial burns.
Meanwhile, London police say they are making "good progress" in the investigation into the bombing on the packed train in Parsons Green, west London.
Assistant Commissioner Mark Rowley said today the public should be reassured and that more police and troops will be on the streets.
He said "we are only aware of one device", referring to the bomb that partially detonated yesterday on the subway train.
Rowley says "we have remnants of that device. We are chasing down suspects".
He refused to provide further details about the bomb, saying an investigation is underway.
Rowley said police are combing through closed circuit TV film and other data, seeking information on the suspected bomber and on possible accomplices.
More to come.