If you get this letter, be afraid
"YOUR life is in immediate danger."
There are few things that could cause terror in someone as much as being informed their life was in grave danger because someone wants them dead.
But that is exactly the warning an increasing number of British people are receiving by their local police force, as a crime wave in some parts of the country has seen big increases in knife and violent crime.
The so-called "Osman warnings" or "threat-to-life" notices are sent to people that police have reason to believe are in danger of being killed - usually by someone known to them.
Last year, 776 of the warnings were sent, a 14 per cent increase on the previous year, but the actual figure is likely to be much higher as nearly a dozen police forces throughout England and Wales did not provide figures.
The scale of the dramatic interventions was laid bare by London's Sunday Telegraph, which obtained the figures in an official information request.
The warnings were linked to cases where police have intelligence to suggest a person is in danger, but don't have enough evidence to make an arrest. So they do the next best thing and warn them.
The letters have been issued for three decades and began after a London man, Ali Osman, was gunned down by a teacher from a school his son attended. His family took the Met Police to the European Court of Human Rights where they successfully argued police breached his right to life by not acting on information the killer was a danger to him.
At one point the teacher told police he was considering a massacre, but no warnings were issued.
The letter is based on a standard template and tells the recipient their life is in "immediate danger".
It goes on to say the threat has not diminished: "The threat remains and we believe has grown with the passage of time. Therefore a serious threat to your life remains."
It advises the receiver to think carefully about who they associate with in the coming days; "who you may, or may not, consider to be your friends", before reassuring them police could help take "active steps" in protecting them and urged them to help investigators.
A spokesman for the UK National Police Chiefs' Council told news.com.au: "Threat to Life Warning Notices are one of a number of options that police forces can use to deal with a situation when there is a threat to an individual's life.
"The police response will always need to be proportionate and will be relevant to the unique factors of any specific threat situation under consideration, taking into account all available information including the level of the threat and how imminent it is.
"Threat to Life Warning Notices have proved highly effective in the overwhelming majority of cases".
The responses range from the person being warned doing nothing at all, to making huge changes to their lifestyle.
While it wouldn't be standard practice to use them in domestic violence cases, it does happen.
"Threat warning notices are suitable for use in domestic violence cases should they be considered an appropriate option based on the information available at the time. It could be considered on a case-by-case basis and implemented as needed," the spokesman said.
The grim notices have been exposed in court cases that involved gangs and drug dealing as police feared drug lords would order the execution of their rivals.
It's not clear how many of the Osman warnings were related to gang activity, but media in the UK report police in regional areas were issuing them as tensions from gang activity in London spread elsewhere.
Police told news.com.au they could not say if the gang activity was linked to the rise in warnings.
London is currently experiencing an explosion of violence that has seen 65 people slain so far this year, a number so shocking it has overtaken New York's murder rate.
In the four years to 2015, just under 2000 notices were issued. But the latest figures show almost half that number have been sent in just 12 months.
Official statistics show last year there was a 22 per cent increase in knife crime and an 11 per cent increase in gun crime.
There have been several high-profile examples of the warnings.
In 2011, Len Gridley received a "threat to life" warning notice after someone threatened to kill him.
"The police sent me a letter and sent someone over to check the safety of my property. When you receive something like that, it puts more things in your mind. You're a bit more aware and safety conscious," he said in a Press Association interview.
Happily for Mr Gridley, police fears for him were never realised.
"As time passes, you can't let it rule your life, otherwise they win. It was a waste of time in my case, but I'm not saying that applies to other people though," he said.
A letter was also sent to Simone Banarjee, the partner of Scottish wife killer Malcolm Webster, which named Webster as a danger to her. He was then under investigation for murder and attempted murder of his partners. He was found guilty in 2011 and jailed for 30 years.
Ms Banarjee told his trial of the moment she confronted him, The Scotsman reported.
"He went very, very quiet and, at that point, I wished I was not in the room," she told the court.