Depends, for a first time buying couple it's a 10% deposit (plus £45k for stamp duty) and then a combined salary of £225k (assuming 4x multiplier on combined income). Sure ~£110k/year is firmly in the top quartile of dev salaries, but not out of the question.

More than likely a couple who are already earning ~£70k/year each probably already have some equity in a current home, so a £1m home might not be much of a step up for them.