A man pleaded guilty on Friday to trespassing at Queen Elizabeth II's London home Buckingham Palace, being caught shortly afterwards with cocaine and a kitchen knife in his bag.

Cameron Kalani, 44, appeared at Westminster Magistrates' Court to plead guilty to trespassing on a protected site, possession of a knife and possession of cocaine during the May 10 incident.

"At 4:30 a.m. the defendant was seen by a fire marshal near Buckingham Palace Road said to be attempting to climb over the fence and trespass into the grounds," said prosecutor Alexander Alawode.

Kalani, who suffers from a mental disorder, climbed over the fence into the estate, before climbing back onto the public Buckingham Palace Road.

"Concerned by the breach of security, palace guards detained him outside the fence a short while later," the prosecution added.

"The defendant was described as confused, not knowing where he was or what was happening."

He is due to be sentenced on December 16.