What a load of hot air.
Under New Labour, Buy-To-Let investment boomed to the extent that at the end of their "reign" almost 13% of all mortgage debt in this country is for Buy-To-Let investments. These investments take properties that would otherwise be bought by first-time buyers out of the market, pushing up the threshold for first-time buyers to enter the market and raising average house prices (i.e. causing inflation).
The NHPAU estimated that by 2007 average house prices had risen by 7.4% purely as a result of Buy-To-Let activity over the previous decade since New Labour came to power.
However, 80% of all BTL purchases are terraced properties and flats, so it is obvious that the price inflation in just that sector of the property market would be much greater than 7.4%.
Don't forget that this price inflation due to Buy-To-Let is added to general house price inflation and other economic pressures affecting mortgage availability. It is no wonder there is an affordability problem, and it is not caused by a lack of new housing construction.
Until this absurd corruption of the housing market is removed, building more housing will simply pump more housing stock into the hands of Buy-To-Let investors who are using housing as a way to make money for themselves without having to actually do anything constructive. They are making that money at the expense of the households who are forced to rent from them because they cannot afford to buy, which is largely because of Buy-To-Let in the first place.
If all the Buy-To-Let properties were converted back to open market properties it would immediately solve the affordability problem for first time buyers, without having to sacrifice one square foot of any hillside to build new ticky-tacky little boxes.