Laila Soueif, lying in a hospital bed after refusing all food for 152 days in a bid to free her jailed son, agreed on Wednesday night to be put on a glucose drip, though it is only likely to delay her full collapse by days.

She told the Guardian she had taken the step as part of a deal she had reached with her children that they would be allowed one chance to intervene before she collapses.

It is likely she will last the next few days, but thereafter she is back to the unknown, and has only been surviving with such low sugar levels because her decline has been a slow process, allowing her body to adapt.

She has been on hunger strike to free her British-Egyptian son, Alaa Abd el-Fattah, from a Cairo jail.

Her son, a writer and activist, has been arrested numerous times and last September he completed his five-year sentence, if his two years in detention before sentencing are taken into account, as is specified by Egyptian law.

She was admitted to St Thomas’ hospital in central London on Monday due to dangerously low blood sugar levels.

A note released by her doctor said there was a high risk of sudden death.

She insists: “I am willing to die and no, I am not personally scared. I am worried about my girls. It is like I feel apologetic to them. But I think by now I am just as effective dead as alive. I think the campaign for his release will go on if I die. It is strong enough that it will continue after I have gone, and so I will have not died in vain.”

Her son knows she is in hospital, but has not been able to communicate with her.

She has lost a third of her weight, her blood sugar reading has dropped and her face in the past fortnight has become noticeably thinner, the lines on her face even deeper than before. Flowers from the Foreign Office and a book on the Palestinians lie by her bedside, which ironically overlooks the House of Commons.

At her bedside are her two daughters, Mona and Sanaa, and other family and friends, many of them Egyptian intellectuals. She insists that once this glucose has been taken, there will be no other infusion until she is unconscious. The doctors, caught in a moral dilemma, have agreed to respect her wishes, including her continued refusal to eat food.

The drip was only agreed after her doctor gave her the stern warning that her organs, in particular her heart and brain, are likely to become permanently damaged. They wrote: “We advise intravenous glucose or controlled refeeding immediately to reduce the risk to herself. The longer the duration of her fasting, the higher the risk of death during the refeeding process, should she cease fasting.”

She said: “I will continue until there is some positive response from the Egyptian government, whether it is allowing my son to have a consular visit or his release.”

There is a faint hope that with the Egyptian state traditionally willing to grant pardons at Ramadan, a new push by the British government might lead to a breakthrough.

But the British prime minister, Keir Starmer, by Thursday had not made a phone call to the Egyptian president, Abdel Fatah al-Sisi, to seek his release. He wrote two letters at the turn of the year. On 14 February he met the family to explain what the government had been doing to secure her son’s release. The family in turn brought a copy of his collection of essays, You Have Not Been Defeated.

At prime minister’s questions this week, before travelling to Washington, Starmer promised he would make the call if necessary, and said there was a feeling in the family: “If not now, when?”

The family feel Sisi is immunised by his advisers from bad news, and it may take an external figure such as Starmer to tell him leniency would be in Egypt’s national interest. But such are the secret wheels of diplomacy, and the bigger Middle East issues at stake, that it may be that Sisi has been refusing to take a call from Starmer.

The family have also had numerous meetings with the Foreign Office, but fear the lack of an all-government effort focused on Sisi rather than the Egyptian foreign ministry has made the lobbying ineffective.

Sanaa Soueif said: “When we met Keir Starmer he asked us for more time and promised that he would do all he could to free my brother and reunite him with his son in Brighton. My sister and I have convinced my mother to take one dose of glucose drip, to try to stop her from dying of hunger today.

“Nothing is guaranteed, but we hope that this gives us a few more days with our mother, and that Keir Starmer keeps his promise.”