Brown joins health secretary Wes Streeting, justice secretary Shabana Mahmood and the two longest-serving MPs in the Commons in speaking out against the bill - although many MPs' views remain unknown.

In an opinion column for the Guardian, external, Brown writes movingly of the death of his first daughter, Jennifer Jane, aged only 11 days, and how this strengthened his belief "this is not the right time to make such a profound decision"

"The experience of sitting with a fatally ill baby girl did not convince me of the case for assisted dying; it convinced me of the value and imperative of good end-of-life care," he said.

Calling for a commission on palliative care, Brown acknowledged that both sides in the assisted dying debate share a common concern and "genuine compassion felt for all those suffering painful deaths".

But with "the NHS still at its lowest ebb", he said "we need to show we can do better at assisted living before deciding whether to legislate on ways to die".

He added: "An assisted dying law, however well intended, would alter society’s attitude towards elderly, seriously ill and disabled people, even if only subliminally, and I also fear the caring professions would lose something irreplaceable – their position as exclusively caregivers."

Responding to his piece, Leadbeater welcomed Brown's opinions and his suggestion of a commission and more discussion of end of life care.

However, she said Britain already has "probably the best palliative care in the world" and insisted her bill already includes the need for a government report on the availability and quality of palliative care.

She said: "He [Brown] and I agree on very many things but we don’t agree on this.

"The need to address the inadequacy of the current law to provide people the choice of a better death and safeguards against coercion, and their loved ones protection from possible prosecution, cannot wait.

"Only legislation by parliament can put right what Sir Keir Starmer calls the 'injustice that we have trapped within our current arrangement.'"