Alex Ritson

Phil Mercer.

Not since the hunger strike in Northern Ireland in 1981, which led to the deaths of 10 Republican prisoners, including the MP Bobby Sands, have so many prisoners in UK jails put their lives at risk.

Four people facing trials related to break-ins or criminal damage by the group Palestine Action continue to refuse food, with two prisoners reaching their 52nd day of hunger on Tuesday.

Palestine Action has become prominent in demonstrations against Israel's military operations in Gaza.

The UK government prescribed Palestine Action as a terrorist organisation in July this year, making any demonstration of support for it a criminal offence.

So far, more than 2,000 people have been arrested for this.

Among them was the Swedish activist Greta Thunberg, who on Tuesday was arrested for holding up a sign reading, ''I support the Palestine Action prisoners.

I oppose genocide.''

Kamran Ahmed is one of the hunger strikers.

His sister Shamina Alam sent the BBC this voice note about his condition.

Lawyers representing Palestine Action have called on the British government to meet them and hear their concerns about their treatment in custody.

But so far, no meeting has taken place.

So just how dangerous are hunger strikes?

Dr Mike Strood is a professor of medicine and nutrition and a specialist on treating prisoners who are refusing food.

My colleague Evan Davis asked him how long the human body can survive not eating.

As long as you're getting liquids, you can withstand usually a minimum of 40 days.

You might die then if you have started off very thin.

Perhaps more usually it's 50 to 60 days and occasionally longer if you started off

overweight, although being overweight doesn't protect you quite as much as you might think.

And what is happening in those, let's say, 40, 50, 60 days as the body adapts to having no nutritional intake?