3.1 In addition to the affordability testing outlined in Chapter 2, the PRA expects firms undertaking buy-to-let lending to have regard to its potential business characteristics. The PRA considers that borrowers with four or more distinct mortgaged buy-to-let properties [Firms may use their judgement when determining how to verify the number of mortgaged buy-to-let properties the borrower has. The PRA recognises that there are a variety of suitable ways to do this including using credit bureau data.], either together or separately, in aggregate, should be treated as 'portfolio landlords'.

3.2 The PRA expects firms to recognise that existing experience and skills acquired in buy-tolet lending do not automatically translate into equivalent skills when assessing portfolio landlords. Lending to portfolio landlords is inherently more complex given the quantum of debt in aggregate, the cash flows and costs arising from multiple tenancies and potential risks of property and/or geographical concentrations.

3.3 These complexities mean that a specialist underwriting approach is appropriate. Firms' underwriting process for portfolio landlords should take a proportionate approach based on their knowledge of the borrower, their portfolio and alternative sources of income they have. Examples of additional information firms may request from the borrower are as follows:

(a) the borrower's experience in the buy-to-let market and their full portfolio of properties and outstanding mortgages;