David Cameron has warned of the "dangers" of an assisted dying law leading to an increase in euthanasia.
Speaking in Leeds as MPs debate the bill in the House of Commons, the Prime Minister said he would not be supporting it but the matter was a "conscience issue".
He said: "I don't see a case for this measure. I don't want to see an expansion of euthanasia in our country. I think there are dangers and so I don't support it.
"If the Bill makes more progress there will be further opportunities to scrutinise this legislation, ask difficult questions about it and to examine the whole subject, which I think is what the nation wants us to do."
MPs have overwhelmingly rejected the Assisted Dying Bill, despite apparent public support.
MPs are set to vote on the right to die for the first time in 20 years today as controversial laws are subject to a landmark debate.
Described by the Archbishop of Canterbury as one of "the biggest dilemmas of our time", MPs are preparing to debate assisted dying.