To be fair, average salary varies per city* and if you earn the average salary in any city*, chances are you'll be able to rent but not buy. I've tried a few London post codes and their average salaries: deep red can't buy can't rent. I've also picked a few random places up north and around Manchester, and it came out orange. I wouldn't be surprised if the conclusion was the same for most of the country!

edit: fixed postcode->city typo.