The UK is on a “slippery slope towards death on demand”, according to the justice secretary ahead of a historic Commons vote on assisted dying.

In a letter to her constituents, Shabana Mahmood said she was “profoundly concerned” about the legislation.

“Sadly, recent scandals – such as Hillsborough, infected blood and the Post Office Horizon – have reminded us that the state and those acting on its behalf are not always benign,” she wrote.

“I have always held the view that, for this reason, the state should serve a clear role. It should protect and preserve life, not take it away.

“The state should never offer death as a service.”

Analysis: Justice secretary’s intervention is potentially embarrassing for the PM

On 29 November, MPs will be asked to consider whether to legalise assisted dying, through Kim Leadbeater’s Terminally Ill Adults (End of Life) Bill.

Details of the legislation were published last week, including confirmation the medicine that will end a patient’s life will need to be self-administered and people must be terminally ill and expected to die within six months.

Ms Mahmood, however, said “predictions about life expectancy are often inaccurate”.

“Doctors can only predict a date of death, with any real certainty, in the final days of life,” she said. “The judgment as to who can and cannot be considered for assisted suicide will therefore be subjective and imprecise.”

Read more: Gordon Brown says assisted dying should not be legalised

Under the Labour MP’s proposals, two independent doctors must confirm a patient is eligible for assisted dying and a High Court judge must give their approval.

The bill will also include punishments of up to 14 years in prison for those who break the law, including coercing someone into ending their own life.

Read more: Where does the cabinet stand on assisted dying?

However, Ms Mahmood said she was concerned the legislation could “pressure” some into ending their lives.

“It cannot be overstated what a profound shift in our culture assisted suicide will herald,” she wrote.

“In my view, the greatest risk of all is the pressure the elderly, vulnerable, sick or disabled may place upon themselves.”

Labour MP Kim Leadbeater, who put forward the bill, said some of the points Ms Mahmood raised have been answered “in the the thorough drafting and presentation of the bill”.

“The strict eligibility criteria make it very clear that we are only talking about people who are already dying,” she said.

“That is why the bill is called the ‘Terminally Ill Adults (End of Life) Bill’; its scope cannot be changed and clearly does not include any other group of people.

“The bill would give dying people the autonomy, dignity and choice to shorten their death if they wish.”

In response to concerns Ms Mahmood raised about patients being coerced into choosing assisted death, Ms Leadbeater said she has consulted widely with doctors and judges.

“Those I have spoken to tell me that they are well equipped to ask the right questions to detect coercion and to ascertain a person’s genuine wishes. It is an integral part of their work,” she said.

In an increasingly fractious debate around the topic, multiple Labour MPs have voiced their concerns.

In a letter to ministers on 3 October, the Cabinet Secretary Simon Case confirmed “the Prime Minister has decided to set aside collective responsibility on the merits of this bill” and that the government would “therefore remain neutral on the passage of the Bill and on the matter of assisted dying”.