On Monday, as the prime minister unveiled a package of measures to boost housebuilding, the housing secretary, Sajid Javid, said ministers had already taken steps to tackle the problem of homes being left uninhabited.

He claimed local authorities had been handed the ability to charge more council tax for vacant properties, adding: “So we’re taking action on that.”

But the Guardian can reveal that the policy outlined in the Autumn budget, to allow councils to double the amount of tax levied on homes if they are left empty, has yet to be enacted.

The campaigner Guy Shrubsole, who runs the Who Owns England group, obtained an email from a government official saying the proposal “is not yet in place since it needs an amendment to primary legislation”.

He uncovered the minutes of a Westminster council meeting that said government officials had “highlighted a potential risk in relation to the government meeting the legislative timetable necessary for a 1 April 2018 implementation”, which could delay action until 2019.

Pointing to the huge number of people sleeping rough on London’s streets, Shrubsole said: “It’s a national scandal that we still have thousands of homes lying empty, many owned by billionaires and offshore firms.

“The government’s unforgivable delay in introducing its promised new empty homes tax means councils will lose out on millions of pounds of revenue that could be spent on affordable housing. And the wealthy owners of empty properties will keep laughing all the way to the bank.”

The Ministry of Housing, Communities and Local Government confirmed there had as yet been no action taken on the policy, saying it would be brought in “as soon as we can”. Meanwhile, a source close to Javid said the cabinet minister’s comments were simply about the proposals that had been announced, adding: “We will bring forward the legislation.”

Among the commitments were: allowing former shops to be turned into homes; basing future planning permissions on developers’ build-out rates; and pressurising councils that fail to produce adequate proposals about the properties they plan to build.

Tackling the problem of empty homes is also seen as critical, which is why the government decided to ramp up the premium that can be charged on council tax from 50% to 100%.

Labour’s shadow housing secretary, John Healey, criticised the delay. “Just like pledges to ban letting agency fees or build new starter homes, ministers have done nothing to legislate for double-rate council tax for empty properties. Their failure to follow speeches with action shows the government is simply not serious about tackling the housing crisis,” he said.

The Liberal Democrat leader, Sir Vince Cable, said Javid had been “boasting about a measure that is apparently unenforceable at the moment”, saying his party would “charge empty homes at 300% as a tougher disincentive”. A freedom of information request by the Lib Dems revealed more than 11,000 homes across the country had been empty for more than a decade.