Security plans for Kate and William's new home in Kensington Palace have been made available to the general public, despite pleas for secrecy from Buckingham Palace.
The former head of Scotland Yard's royal protection squad told the Evening Standard he is "speechless" that such sensitive documents can be seen by anyone with a passport or driving licence.
The Palace submitted plans to the Kensington and Chelsea council for renovation permits for Princess Margaret's former apartment, where the Duke and Duchess of Cambridge are due to take up residence next year.
Among the security upgrades included in their application are an dirty-bomb proof "air lock" double-door system, an advanced CCTV system, pop-up bollards and spiked railings.
Dai Davies, former head of the London police royal protection squad, said "it's unbelievable" that the security measures have been allowed into the public sphere.
"It beggars belief at the level of incompetence by those who purport to be experts in security," he said.
"The problem you have got is not just terrorists, it's 'fixated persons'. There is a list at Scotland Yard of people who have an unhealthy interest in the royal family. You wouldn't want someone like that getting hold of it."
The basic application for renovations are available on the council website, but to view the actually details requires a trip to city hall with proof of ID. There are about half a dozen "Kensington Palace" applications on the website from the last few months, with directions on how to view further information.
Buckingham Palace had sent a letter to the council asking that their applications regarding Kate and William's new home be treated "as confidential." A council spokesperson defended their policy of making plans public, saying they were following government rules.