21 percent of dwellings. 89 percent of landlords were private individual landlords, 5 percent were company landlords, and 6 percent were ‘other organisation’ landlords. These were responsible for 71 percent, 15 percent and 14 percent, respectively, of all dwellings in the sector. 22 percent of landlords had let properties for three years or less with two-thirds (69 percent) for 10 years or less. Only 5 percent had let for more than 40 years. In terms of formal letting and management practices, nearly all landlords and agents (97 percent) made use of a written tenancy agreement, with 91 percent requiring a deposit, and 84 percent requiring tenants to provide a reference. Arrival of institutional involvement in sector Institutions such as pension funds and insurance companies have been very active in residential investment in countries such as Germany and the United States where private rented residential property accounts for a much larger part of the overall residential stock (Germany 60 per cent and US 32 per cent). In contrast, the United Kingdom saw limited involvement until more recently, due to a long-standing fear of rent control and other reputational concerns related to the ownership of rented residential property. Since January 1990, the percentage of UK housing stock in the private rented sector has grown from 9 per cent to 19 per cent but mostly due to the growth in the residential buy to let investor, who either purchases the property outright, or applies to a bank or building society, and gets a buy-to-let mortgage on the property. Since 2010, UK institutions have taken a serious interest in the private rented sector, in part encouraged by their positive experiences in the private student accommodation market. The potential for high and continued rental streams, linked to general inflation, has attracted institutions seeking to match their liability profiles. Investors have looked to other more established private rental markets to identify the best practices adopted. This has seen the development of the build-to-rent (B2R) concept into the UK which follows the service-led culture of the multi-family sector in the United States. The involvement of different investors now ranges from the individual landlords owning buy-to-let properties and houses of multiple occupation (HMO), through to various housing associations, which now provide properties for around 6 million tenants in the United Kingdom, and the property companies who operate large scale rentals, that have become the UK institutions which created