Bishops Avenue, in North London, dubbed the “Billionaire's Row” is one of the wealthiest streets in the world. The average value of a property here is around £5 million, but some of the more grander mansions cost many times more. The palatial Toprak Mansion, for instance, originally owned by the Turkish tycoon Halis Toprak, was bought by the President of Kazakhstan in 2008 for £50 million making it one of the most expensive houses in the world.