Al-Qaeda is encouraging terrorists to mount bomb attacks at Epsom Downs Racecourse when the Queen and tens of thousands of spectators attend the Derby.
Inspire, an English-language magazine published by Al-Qaeda in the Arabian Peninsula, has published an article encouraging jihadists returning from the civil war in Syria to become suicide bombers or use car bombs to inflict mass casualties at key sporting events.
In addition to the Epsom Derby, the magazine mentions Wimbledon, football matches and the Savoy Hotel as suggested targets.
The racecourse confirmed this morning that it is taking the threat seriously, while police said they are aware of the websites disseminating this material and "appropriate steps have been put in place" by MPS counter terrorism command.
Someone calling themselves AQ Chef, wrote in the magazine: "In the beginning of the summer, we have Cheltenham, and the end of the summer we have Epsom, whereby horse races are attended by thousands from around the kingdom including the Queen."
It advises would-be terrorists to: "Disguise yourself during the operation, appear fat (add some clothes on to you) change your complexion, be a ‘clone’, use any mask (believe me embarrassment is the last thing you will think about)."
It said: "When targeting high profile places, go for the entrance; you cannot get a car into most of these targets".
America is seen as the primary target followed the UK, France and other "crusader countries".
Johnno Spence, spokesman for Epsom Downs Racecourse, said this morning it was aware of the article and is taking the threat seriously.
Mr Spence: "We have a strong relationship with the police in terms of royalty with her majesty the Queen attending Derby Day. It will be very much led by them, but security at the Derby is clearly hugely important and always under review.
"In terms of Epsom Downs Racecourse, this is a matter of national terrorism and therefore we will be guided by the police. We constantly review and monitor the security."
The Queen arrives at the Epsom Derby in 2012
A Metropolitan Police Service (MPS) spokesman said: "The MPS counter terrorism command is aware of the websites and appropriate steps have been put in place, including providing security advice where relevant.
"The public is reminded that viewing downloading or disseminating extremist material within the UK may constitute an offence under Section 1 and 2 of the Terrorism Act 2006.
"As part of our continued work, we regularly work with, and support, industry, the organisers of sporting events and companies overseeing crowded places with a variety of briefings and advice."
Last year was the centenary of the death of suffragette Emily Davison who ran out in front of the King’s horse and there were concerns that militant feminists might disrupt the event.
But despite national media reports of a greater police presence to counter this threat, no extra police were deployed and the event passed off without any disruption.
The Queen regularly attends the Epsom Derby which will be held on June 7 this year.