"It is difficult especially to see how either a lifetime fixed rate mortgage or 30% discount for first time buyers - effectively a right to buy on private property - would work in practice. "
Under the plan, buyers would need a 5% deposit and the mortgage repayments would then remain the same throughout the lifetime of the mortgage.
As part of the announcement, the Conservatives also promised to launch a 'First Home' scheme, giving first-time buyers a 30% discount on new homes in their local area.
Boris Johnson also announced plans to build "at least" one million new homes over the next five years, end no fault evictions, and launch 'Lifetime Rental Deposits' which can be transferred between rental properties.
Boris Johnson said: "At the moment, renting a property can also be an uncertain and unsettling business, and the costs of deposits make it harder to move. We are going to fix that.
"We will end no fault evictions, so that landlords can't remove tenants without good reason, and introduce Lifetime Rental Deposits so renters don't have to save up for a new deposit while their money is tied up in an old one."
Vadim Toader, founder and CEO at Proportunity, commenteed: "Homeownership remains the aspiration of the majority of Brits and it is right the Conservatives are looking at new ways of getting people on the housing ladder but it's vital any new proposals are in fact workable.
"It is difficult especially to see how either a lifetime fixed rate mortgage or 30% discount for first time buyers - effectively a right to buy on private property - would work in practice and it is telling the Tories are promising only a million homes when their target is 300,000 new homes a year."