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”.

With six days to go before Friday’s historic Commons showdown on assisted dying, it’s the opponents who are turning up the heat.

The explosive attack on the bill by Shabana Mahmood follows the poignant and personal plea from Gordon Brown to MPs to reject the bill.

We knew the justice secretary is opposed to the bill. She has already made that clear. But her attack on it, in a letter to constituents, is brutal.

Read more: UK on ‘slippery slope’ to ‘death on demand’, warns justice secretary

She talks about a “slippery slope towards death on demand”. Savage. The state should “never offer death as a service”, she says. Chilling.

So much for Sir Keir Starmer attempting to cool the temperature in the row by urging cabinet ministers, whatever their view, to stop inflaming or attempting to influence the debate.

Ms Mahmood talks, as other opponents have, about pressure on the elderly, sick or disabled who feel they have “become too much of a burden to their family”.

She hits out at a “lack of legal safeguards” in the bill and pressure on someone into ending their life “by those acting with malign intent”.

Malign intent? Hey! That’s quite an assertion from a secretary of state for justice and lord chancellor who’s been urged by the PM to tone down her language.

It’s claimed that Sir Keir ticked off Wes Streeting, the health secretary, after he publicly opposed the bill and launched an analysis of the costs of implementing it.

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

Will the justice secretary now receive a reprimand from the boss? It’s a bit late for that. Critics will also claim Sir Keir’s dithering over the bill is to blame for cabinet ministers freelancing.

Shabana Mahmood is the first elected Muslim woman to hold a cabinet post. Elected to the Commons in 2010, she was also one of the first Muslim women MPs.

She told her constituents in her letter that it’s not only for religious reasons that she’s “profoundly concerned” about the legislation, but also because of what it would mean for the role of the state.

But of course, she’s not the only senior politician with religious convictions to speak out strongly against Kim Leadbeater’s bill this weekend.

Gordon Brown, son of the manse, who was strongly influenced by his father, a Church of Scotland minister, wrote about his opposition in a highly emotional article in The Guardian.

He spoke about the pain of losing his 10-day-old baby daughter Jennifer, born seven weeks prematurely and weighing just 2lb 4oz, in January 2002, after she suffered a brain haemorrhage on day four of her short life.

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

Mr Brown said that tragedy convinced him of the value and imperative of good end-of-life care, not the case for assisted dying. His powerful voice will strongly influence many Labour MPs.

And what of Kim Leadbeater? It’s looking increasingly as though she’s now being hung out to dry by the government, after initially being urged by the government to choose assisted dying after topping the private members bill ballot.

All of which will encourage Sir Keir’s critics to claim he looks weak. It is, or course, a private members bill and a free vote, which makes the outcome on Friday unpredictable.

But the dramatic interventions of the current lord chancellor and the former Labour prime minister are hugely significant, potentially decisive – and potentially embarrassing for a prime minister who appears to be losing control of the assisted dying debate.