By property tax, I assume you mean council tax?? In which case, that isn't entirely true. An unoccupied and unfurnished property MAY qualify for a discount but it depends on the local council.

For Clerkenwell, I assume the property falls under Islington council. Their policy is that from 1 April 2013, the discount and exemptions for empty properties and second homes will end.

A full council tax charge will be applied to:

Second homes
Unoccupied but furnished properties
Properties undergoing major repair or structural alteration
Properties which are unoccupied and substantially unfurnished for less than two years

A 50% council tax premium will be charged on properties left empty for two years or longer. This is known as the 'empty homes premium'.