Scotland Yard is investigating after a letter containing white powder purporting to be anthrax was sent to Meghan Markleat Kensington Palace.

The letter, addressed to her and fiancé Prince Harry and understood to contain a racist message, led to a security scare, with specialists rushed in to check the powder.

Measures already in place meant the package was intercepted before it reached the couple. Meghan, 36, and Harry, 33, are understood to have been informed.

Officers from the Metropolitan Police’s counter-terrorism command were called in after the letter was received on February 12. It was delivered to St James’s Palace for sorting. Analysis of the powder found it was harmless.

The letter was sent to Kensington Palace on February 12 (AP)

On February 13, police revealed a package containing white powder had been sent to Parliament, reportedly to the office of Home Secretary Amber Rudd.

The material was also found to be harmless. Police are believed to be examining whether the incidents are linked. There have been no arrests.

The palace letter is being played down officially by police but it has put the Met on high alert before the wedding in Windsor in May.

Security for the day is under constant review, with potential threats ranging from a terror attack to that posed by obsessed individuals.