Whenever you propose reform of private renting, the landlord lobby always says no, because "landlords couldn't afford it". Whether it's asking landlords to cover the cost of letting agent fees, to apply for a licence, to charge controlled rents, or to pay tax on their loans, we're asked to believe that they can't afford it. Then they threaten to raise rents - as if rents haven't already been outpacing inflation since the end of the recession.

This claim assumes that landlords are already paying large amounts of their revenue out again in costs. Some of them are, but we point out that the majority are not, because they don't have a mortgage.

For example, an interest-only mortgage of £150,000 at 4% costs £6000 a year. Rent on the £200,000 property bought with that mortgage might get you £10,000. Two thirds of private rented properties have no mortgage, and thus have significantly lower costs and capacity to absorb new regulatory requirements.

Where do we get this figure from? The Council of Mortgage Lenders. They said back in 2013 that there were 1.46m buy-to-let mortgages. At that time there were 4.0m private rented households in England (source), 0.32m in Scotland (source), 0.19m in Wales (source) and 0.12m in Northern Ireland (source). That's 4.63m privately rented homes in the UK as a whole - 31.5% of which have mortgages on them.

"But Dan," I hear you say, "that figure is three years old now". True: the CML doesn't seem to have published a more up to date stock of buy-to-let mortgages since then. But we can estimate how it has changed during that time.

The Tenancy Deposit Scheme reports that the number of deposits protected in England and Wales increased by around 760,000 between March 2013 and March 2016. In the same period, the CML records 333,200 properties bought with a buy-to-let mortgage (data available here). If there are now 5.39m privately rented homes in the UK (and this number doesn't account for growth in Scotland or Northern Ireland) and 1.79m mortgages (assuming none of the original 1.46m mortgages have been paid off), then still only 33% of private rented homes are mortgaged.

With HM Revenue & Customs stamp duty statistics now recording how many transactions are of second properties, we will start to know more about how many people are buying homes to rent out - with a mortgage, and without.