The amount people are allowed to borrow against salary is a factor, but price is essentially driven by supply and demand and there simply isn't enough housing in this country.
When I bought my first flat around 20 years ago, I had a choice. Northern Rock were offering mortgages 8 times your salary!
That sounded ridiculous to me, but I was lucky to have a choice and borrowed around x 3.5 times my salary to purchase my first flat.
People in their early 20's don't have that luxury or choice now. There is no affordable housing. I've posted further down that the cheapest 2 bedroom houses in Hazel Grove are £210,000 and there aren't many options! That is 8 times the average salary of someone in their early 20's.
Rents are sky high too, but people need to live somewhere.
What choice do young people have? Stay at their parents forever?