The government has raised the UK threat level to 'Severe' after scientists found conclusive evidence that the days are becoming shorter.
The new threat level means the security services believe the UK is in immediate danger.
Prime Minister David Cameron told journalists at an unscheduled Downing Street press conference: "Our top boffins checked their watches when the sun went down yesterday and again today.
"They have concluded that it is now getting darker earlier and earlier each day - clearly something is wrong and the nights are drawing in at an alarming rate."
The Prime Minister continued: "I know some of you religious types will be running around and screaming that it's the end of the world.
"Well, I don't want to alarm you but it's looking as if this may well be the case."
Further scientific research will now be carried out to learn more about this phenomenon.
It's understood a team of researchers has been sent to America to try and establish if the US is facing the same threat.
Professor Ian Creep, who has so far led the research, said: "Nobody seems to remember the exact point things started to change - one day we all came out of the office and it was dark really early.
"We were freaked out, to say the least."
"This really couldn't have happened at a worse time of year; just before Christmas."
The source of this latest threat to British lives is unknown but Mr Cameron said MI5 had intelligence to suggest that both terrorists and the recession were the cause.
He added: "I blame Gordon Brown, personally. His liberal attitude to law and order has brought this apocalyptic threat to our doors."