Why is there such a lack of affordable housing in the UK?

The main reason - is house prices are out-pacing peoples wages - making it more and more difficult for people to afford to buy houses. Banks and building societies will only lend so much money to new lenders. If they want large houses, they have to pay a sizeable deposit.

Council houses used to be 'the affordable alternative' BUT - with council tenants now having the 'right to buy' lots of people are staying put - reducing the availability of council properties for rent.