Internment: Could it help fight terrorism?
In the wake of the Manchester suicide bomb attack a former assistant commissioner of the Metropolitan Police has called for the reintroduction of internment camps.
With security services revealing there are 3,000 people engaged in plots in the UK and as many as 23,000 who have appeared on the radar of counter-terror agencies, Tarique Ghaffur - in charge during the 7/7 bombings - wrote in the Mail on Sunday that "a proper national debate" should take place.
But what would such a policy entail?
What is internment?
Internment is when people are imprisoned without trial.
It is often associated with wartime situations, or when foreign nationals or people with strong political stances are detained.
When has it been used in the past?
The most famous use of it in the UK was during the Troubles in Northern Ireland.
The British Army began Operation Demetrius in 1971, which involved the mass arrest and internment of 342 people suspected of carrying out tasks for the IRA.
The government-approved policy was in place until 1975, during which time 1,981 people were interned.
Internment was also used during both World War One and World War Two. Both sides set up internment camps to detain civilians with sympathies to the enemy cause.
For the first two years of the Second World War, around 8,000 people deemed enemy aliens were temporarily interned in British camps before being deported to the colonies.
A more modern example of an internment camp is Guantanamo Bay in Cuba, used by the US to detain terror suspects after the attacks on 9/11.
How could it work?
Mr Ghaffur proposed setting up specialist centres to detain the 3,000 extremists.
He said they would be community-based centres where the internees would be "risk-assessed and theologically examined".
Once this step was taken, they would then be made to go through a deradicalisation programme, using the expertise of imams, charity workers and counter-terrorism officers.
Those who could be deradicalised should then be "carefully allowed back into the community," said Mr Ghaffur, but those "deemed too dangerous should be locked up".
He said the centres would need to have oversight from vetted Muslim and other community leaders.
What is wrong with the proposal?
Some people backed Mr Ghaffur's stance, including a former head of the government's emergency council Cobra, Colonel Richard Kemp, who said the UK's police and intelligence services simply could not monitor everyone they needed to.
But there is fierce opposition to his plan as well, with figures such as ex-Scotland Yard chief Lord Blair rejecting the idea as counter-productive.
Martha Spurrier, director of rights group Liberty, said: "We're a civilised country. We believe in the rule of law - suspects knowing the case against them, standing trial and, if found guilty, being sent to prison by a judge.
"This is the foundation of our free, democratic society - the exact thing terrorists want to destroy.
"Countering the scourge of extremism will clearly be a priority for the next government - but they can and must do so while protecting our values more vigorously than ever."
What is the current law around terror suspects?
The police can hold a person for up to 24 hours before they have to charge them with a crime or release them.
They can apply to a court to hold a person for up to 36 or 96 hours they are suspected of a serious crime, such as murder.
But if a person is arrested under the Terrorism Act, they can be held without charge for up to 14 days. Police would then have to return to the courts for any extension.