Your numbers aren’t right here. Mortgages are typically available at about 4-4.5 times salary. Two people earning 50k each would be able to borrow about £400,000. To get a mortgage of £225k requires two people to be earning more like 50k between them, i.e. £25k each. Indeed, one of the reasons house prices have risen so much is precisely because of this availability of mortgages — the average couple can afford the average house price based on the average mortgage multiple. Buy-to-let has certainly been a nasty upwards pressure on houses, but they comprise a minority of homes (about 25-30%).
There are some misunderstandings about “tenant pays for the mortgage” thing too. The average UK rental yield is 3.6%. Mortgage rates are typically in the ballpark of 3%. However, you have to load the capital cost of the deposit in to the calculation and owning property is pretty expensive in terms of management fees, repairs and so on too. Basically, the average income from rent will, typically, roughly cover the average cost of the debt and equity put into the property. Could be more, will often be less. However, even if the rent covers these costs, that isn’t “paying for the mortgage”, because the debt still has to be paid off.
So then people think they’ll make money on the capital gain of the property. Trouble there is that the frictional costs are very high. They’ll have paid 3% stamp duty on top of the basic stamp duty on purchase, plus solicitor fees. On sale, they’ll pay estate agent fees. If the property rises in value enough, they’ll pay capital gains tax at top rate — you either sell the property or you don’t, so there is no chance to phase the capital gain to avoid the CGT. However, average property rises in typical BTL properties have not been anywhere near as much as you might guess over the last 10-20 years. There have been some eye watering rises but there are also been some periods of crash. It’s very regional.
My experience with people generally and landlords in particular is that almost none of them do (or even know how to do) the financial calculations properly to genuinely compare this stuff. Landlords often think they’re making money by renting out a property whereas they actually aren’t. Property returns in reality are actually pretty shitty. Net of all the things I am talking about, the result over the last 10 years or 15 years or 20 years will have been noticeably worse than putting the same money into the stockmarket, say.
Now, you might wonder about the point of saying all this. It’s certainly not to suggest that there is nothing to worry about or that BTL isn’t a problem. BTL is a massive problem! It’s more that I think the myth of landlords making easy money is actually feeding the problem. People who have some spare money to invest just default to buying property because they don’t know about anything else and everybody is telling them that this is the easy way to do it. My hope is that countering that propaganda might slowly help to defuse the situation.