In many parts of the UK there are substantial freeholders who historically have owned and continue to own large land holdings, and this ownership has been and continues to be passed under leased ownership to sub-landlords and leaseholders; this system was particularly suitable when areas of London were initially built on greenfield land, and later in the period immediately after the Second World War, when considerable renovation and rebuilding was urgently required, the estates were able to effectively subcontract redevelopment to sub-landlords, known as head-lessors.