Renee Joubert, Euthanasia-Free NZ executive officer, said the House of Commons decision sent a "clear message" to New Zealand.
British MPs voted 330 to 118 against changing the law to allow doctors to help terminally ill people die.
"It is a waste of time to debate an assisted suicide bill at committee stage because no safeguards can ever be safe enough," Ms Joubert said.
"As several MPs remarked, it is simply impossible to prevent vulnerable people from coercion and internal pressure to request death."
Ms Joubert said there was "no way" any third party could be certain a person made a truly free and voluntary request for assisted suicide.
Euthanasia-Free NZ said an ongoing Health Select Committee inquiry was an important step in determining the real needs of suicidal New Zealanders and how they could be cared for more effectively.
The British decision was a setback for the Voluntary Euthanasia Society, spokesman Dr Jack Havill said today.
"We're very disappointed because we thought maybe that would help us make decisions in New Zealand."
However, Dr Havill said passage of a law legalising assisted dying was inevitable in Britain.
He compared the issue to slavery, saying centuries ago British lawmakers rejected a bill to abolish human enslavement before changing tack.
Dr Havill said the bill shot down in the House of Commons was flawed.
"They were suggesting that they'd have to have a judge, a High Court judge, to be involved in the decision-making. That's quite frankly stupid."
Lawmakers in California were moving in the opposite direction from the British.
California's Senate passed a new assisted-dying bill by 23 votes to 14.
Dr Havill said he was "very pleased" about the Californian decision.
If the state's governor Jerry Brown signed the bill, California would follow Montana, Oregon, Vermont and Washington in legalising some forms of assisted dying.
A Democrat in the state Senate said the new law advanced individual liberty and freedom of choice.
But The New York Times said a Republican senator told the Senate the new law would unintentionally end up pushing "the old or the weak out of this world."
On June 23, local supporters of voluntary euthanasia, including Ms Seales' husband Matt Vickers, presented a petition to Parliament.
Mr Vickers attended the Voluntary Euthanasia Society's presentation of the petition, which had some 9000 signatures and called on lawmakers here to renew discussion about the right to die.
Prime Minister John Key previously said any vote in Parliament on the issue would rely on individual MPs taking a conscience vote.
Support and opposition for euthanasia here has not followed neat, party-political lines.
When Mr Vickers presented his petition, individual MPs from the Act, Green, Labour and National parties came to show their support.
- NZME
