Hollywood stars have pleaded with Liz Truss to intervene to help free a British-Egyptian pro-democracy activist as he marks the 74th day of his hunger strike.

Dame Judi Dench, Emma Thompson, Mark Ruffalo and Carey Mulligan are among the signatories of a letter directed at the Foreign Secretary and her US counterpart in aid of Alaa Abd El-Fattah.

Mr Abd el-Fattah, 40, has spent most of the past decade behind bars in Egypt and last December was sentenced to five years in prison after being accused of spreading false news.

His sister, Sanaa Seif, and friend Khalid Abdalla, the actor who plays Dodi Fayed in The Crown, were among those to raise the case at a press conference in the Houses of Parliament on Tuesday.

Alaa is slowly dying and hopefully we can save him, I know we have a window of opportunity to save him

They were joined by the families and MPs involved in other cases of British nationals detained abroad who want the Foreign Office to act with greater urgency to free their loved ones.

Ms Seif said: “Today marks the 74th day of Alaa’s hunger strike, my brother is slowly dying in his prison cell but he wants to live.

“He misses his life, he misses his job, he misses his son, and us.

“Alaa started his strike only drinking water and taking rehydration solutions, then on day 55 the Egyptian authorities made a small compromise – they moved him to a prison where there is a bed to sleep on, he slept on a bed for the first time in three years and was allowed books for the first time in three years.

“He also made a little compromise from his side and switched to what he calls Gandhi-inspired hunger strike – he started taking 100 calories a day, basically to gain us more time in the campaign for his release.”

Ms Seif noted the average daily calorie intake for a person is 2,000, adding: “We’re deeply puzzled by the way we’ve been treated by the Foreign Secretary, Liz Truss. Why hasn’t she met with us? Why has she still not made an official statement about Alaa? I can tell you it hurts.

“Alaa is slowly dying and hopefully we can save him, I know we have a window of opportunity to save him.”

Ms Seif said she believed Foreign Office minister Lord Ahmad of Wimbledon was “genuinely sympathetic” when they met but insisted the UK needs to make a high-level intervention.

She explained there is a route which could see her brother deported if he renounces his Egyptian citizenship, noting he is prepared to do this.

Ms Seif added: “How it could be resolved is a high-level call from Prime Minister Boris Johnson, but also followed with firm negotiations from the Foreign Secretary.”

Mr Abdalla said more than 1,000 people, including “pillars of cultural landscape”, have signed the letter to Ms Truss.

He said: “It’s an extraordinary thing to be here as a signatory of that letter but also as a friend of Alaa directing that strength to her – if all of these people can sign this letter, how can it be that Liz Truss is not answering? It hurts, as Sanaa says, on a deep level.”

In the letter addressed to Ms Truss and Antony Blinken, it states: “We call upon you to use all diplomatic power to leverage the importance of your strategic relationships with Egypt to secure his immediate release.

“As public intellectuals, artists and human rights defenders, we are appalled to see the inhumane treatment of Alaa, whom we consider a peer, as he continues to be held arbitrarily in Egyptian prison.”

Shadow foreign secretary David Lammy called on Ms Truss to meet with family of Mr Abd el-Fattah, who live in his Tottenham constituency.

Raising concerns over the Foreign Office’s wider response to families, he said: “The approach seems haphazard, arbitrary, sometimes lacking resource, sometimes unco-ordinated and certainly lacking transparency and a sense of a systematic approach to these families that find themselves in this condition.”

Richard Ratcliffe, whose wife Nazanin Zaghari-Ratcliffe was detained for six years in Iran, said the “sympathy but no traction” experienced by many relatives was a familiar story to him.

He said: “Part of me wanted to be here to say ‘listen, there is another side, you keep battling but you will get them home, you will get out of this’. It’s not quick and in our case it took a lot longer than we expected but it is through solidarity, you feel so alone at the beginning of this but together we get through this.”

Leila Fitton, 31, from Bath, via video message, said her father Jim Fitton, 66, a retired geologist, had been subjected to a “highly-political, unfair and ridiculously harsh verdict” after he was jailed for 15 years in Iraq on allegations of attempted artefact smuggling.

Other cases to be raised included: Jagtar Singh Johal, of Dumbarton, West Dunbartonshire, a Scottish Sikh who was arrested in India on November 4 2017; and Peter Jouvenal, 66, a British journalist arrested by the Taliban in Kabul six months ago.