Simon Cowell's London Mansion Burgled.Music mogul SIMON COWELL's London home was ransacked while the star was away in America.The American Idol judge is devastated after thieves raided the Holland Park pad, making off with jewellery, silver, and electrical equipment.Cowell has been branded "unwise" by police after he left his house keys with building constructors who were refurbishing his £6 million house.Local police who investigated the crime say, "It was an unwise decision to say the least. You wouldn't believe some of the things Mr Cowell had accumulated over the years that the thieves took a fancy to."A source tells British newspaper The Daily Express, "What has happened in similar cases is that someone copied the main key. I'm sure the builders would have been very careful about who had access, but it's not always easy when a number of sub-contractors are coming in and out of the place.