Laila Soueif, who has been consuming only herbal tea, black coffee and rehydration salts, has lost 35% of her body weight since beginning her hunger strike in September.

Her family wants UK Prime Minister Sir Keir Starmer to telephone the Egyptian President, Abdul Fattah al-Sisi, to resolve the case of her son, whose latest five-year sentence was due to have ended last September.

“If Keir Starmer would pick up the phone and speak to President Sisi, I believe that he can secure the release of my brother, and save my mother’s life,” her other daughter, Sanaa Seif, said in a statement on Wednesday morning.

“Keir Starmer has to make this call today. Every moment that he waits means that my mother is more likely to die.”

After meeting Laila Soueif earlier this month, Sir Keir vowed to “do all that I can to secure the release of her son Alaa Abdel Fattah and reunite him with his family”.

“We will continue to raise his case at the highest levels of the Egyptian government and press for his release,” he added.

Alaa Abdel Fattah, a 43-year-old blogger and pro-democracy activist is one of Egypt’s best known political prisoners.

He was arrested in September 2019, six months after finishing a previous five-year sentence.

He was convicted in 2021 of “spreading false news”, for sharing a Facebook post about torture in Egypt.

The Egyptian authorities are refusing to count the more than two years he spent in pre-trial detention towards his time served.

Although he acquired British citizenship in 2021, Egypt has never allowed him a consular visit by British diplomats.

His own hunger strike in 2022, as Egypt hosted a UN climate conference, led to international pressure for his release and an improvement in his conditions in jail.