Homeowners who leave properties empty should be hit by a 500% premium on council tax bills to help tackle the housing crisis, says Sir Vince Cable.
He claimed there was “little recognition” in government of the "radical change" needed to resolve the shortage of homes.
Under Lib Dem plans, overseas buyers would pay a stamp duty surcharge that could be based on a proportion of the value of the building.
Struggling first-time renters under 30 would be able to apply for government-backed loans of up to £2,000 to help them with upfront costs, such as deposits.
It comes as the government confirmed a £1.67 billion investment deal for 23,000 new affordable homes.
'Greedy' landlords give a bad name
"At one extreme are individuals with serious mental health issues and tens of thousands of homeless families trapped in unsuitable 'temporary' accommodation," said Sir Vince.
"At the other, millions of mainly young people who, despite being in good jobs, struggle to pay the deposits or rents required for satisfactory rented accommodation or to afford home ownership.
"As we build more homes, millions will continue to live in the existing stock of social housing, privately rented property and owner-occupied property, many of them faced with poor conditions, unaffordable rents and instability."
He added: "We need an end to exploitative, greedy, negligent or neglectful practices in the private sector, which give the majority of good landlords a bad name."
Tougher sanctions required
Speaking to Julia Hartley-Brewer, he mentioned the "ideological struggle" between previous governments.
"For Labour, council housing is good and private is bad, and for Tories it’s the other way around," he said.
We need a combination of things - a lot more council housing and more affordable private housing. Building properties that can be rented and the rent converted to private ownership.
"I’m talking about is bridging the gap between private and public and letting non-profit developers do unconventional things."
On his proposed 500% premium on homeowners who leave properties empty, he explained it would only apply to investors and not those "moving for perfectly good economic reasons".
"There is a penalty attached to properties unoccupied for long periods of time. But they make little difference to investors who are looking for appreciation of price so you need more penal sanctions.
I think there’s a difference between encouraging people to invest for productive purposes and investing in property so the price can go up.
We’re not talking about people moving for perfectly good economic reasons. We’re talking about people investing in property."
'Ambitious plans' to fix housing
At least 12,500 of the new properties being built under the government investment deal will be for social rent in high-cost areas.
Housing, Communities and Local Government Secretary James Brokenshire said: "The Government has ambitious plans to fix the broken housing market and build the homes our communities need.
"Today's announcement is a further milestone. It will secure the delivery of an additional 23,000 much-needed affordable homes as well as paving the way for a new generation of council houses.
"The majority of these new homes will be in high-cost areas helping to ease the burden of rent on hard-working families and delivering stronger communities."