Ministers have been warned not to lose interest in the case of the British-Egyptian pro-democracy activist who is on hunger strike in jail, if they want to save his life.

Former British ambassador to Cairo John Casson said the Egyptian tactic of playing for time as ministers show they are “all talk” over Alaa Abdel-Fattah appears to be working.

He also accused Foreign Secretary James Cleverly of “gaslighting” the writer by engaging with the Egyptians’ claims that he is not formally a British citizen.

Mr Cleverly told MPs on the Foreign Affairs Committee on Monday that he remained “interested” in the case, but this language was contrasted with him previously having said he would work “tirelessly for his release”.

Mr Casson, who represented British interest in Egypt for four years until 2018, said “things are still looking pretty grim” after the family received a letter from the writer suggesting he is still alive.

“If we think about where we were last week, the Prime Minister went to Egypt and he said to the president of Egypt the persecution of this British national has got to stop, and in the week since it has become clear that Egypt is playing for time and are banking on our ministers losing interest and being all talk,” he told BBC Radio 4’s Today programme.

“It looks like it might be working. Yesterday we went from the Foreign Secretary, who 12 days ago was saying he was working tirelessly for Abdel-Fattah’s release, to yesterday saying he remained interested in the case and talking as if it’s just a procedural disagreement between friends.

“The Egyptians understand power and they will be smelling the weakness in what the Foreign Secretary said yesterday.”

Mr Cleverly had told the select committee that the UK was unable to get consular access to the citizen because of a “difference of opinion” centring on the Egyptians not accepting that Mr Abdel-Fattah has completed the administrative process in the Egyptian system for dual nationality.

Mr Casson said: “Every time anyone gives airtime to that Egyptian talking point it is gaslighting, it’s like when an abuser tells a person who is being abused that they’re responsible or it’s not really abuse.

“We need to be clear, it’s daily persecution of a British national by the very Egyptian officials that the Foreign Secretary is talking to.

“If we want to save his life we need to show that the longer this goes on the more serious it will get, not the less serious.”

He urged the Government to escalate the situation from talking and requests, to putting Mr Abdel-Fattah as the “defining issue” of relations with Cairo, with the Government “spelling out clearly the consequences” of any further harm to him.

Concerns for Mr Abdel-Fattah were growing after he stepped up a hunger strike and stopped taking water in protest at his treatment by the Egyptian authorities.

Prison officials last week refused to allow a lawyer for the family to visit him after the authorities told his mother they had made an unspecified medical intervention.

On Monday, however, his sister Sanaa Seif tweeted: “I’m so relieved. We just got a note from prison to my mother, Alaa is alive, he says he’s drinking water again as of November 12th.

“He says he’ll say more as soon as he can. It’s definitely his handwriting. Proof of life, at last. Why did they hold this back from us for 2 days?!”

Mr Abdel-Fattah escalated his protest to coincide with the start of the Cop27 climate change summit in the Egyptian resort of Sharm El-Sheikh, in the hope of focusing the attention of the world on his plight.

He has spent most of the past decade in prison and is currently serving a five-year sentence on charges of disseminating false news, for retweeting a report in 2019 that another prisoner died in custody.

For the past six months he has been on a partial hunger strike, taking just 100 calories a day.