Homeowners who deny inspectors access could face criminal prosecution and a fine of up to £200.

While refusing to supply requested information without a “reasonable excuse” could attract a fine of as much as £500.

The levy, formally called the high-value council tax surcharge, was announced by ex-Chancellor Rachel Reeves at last year’s Budget.

Properties valued above £2million could be charged as much as £7,500 more per year, depending on their worth.

London and the South East are expected to bear the brunt of the policy, though expensive rural properties will also be caught up in the raid.

Shadow Chancellor Sir Mel Stride has branded the enforcement measures a “sinister assault on civil liberties.”

“We may have changed Prime Minister, but it’s the same old story with Labour – how can we raise taxes to pay for more benefits? Now they have chosen a sinister assault on civil liberties as their latest method,” he said.

‘Andy Burnham and Angela Rayner are sending their council tax police to people’s homes so they can drag them into paying their new family homes tax,’ Mel Stride said

“Andy Burnham and Angela Rayner are sending their council tax police to people’s homes so they can drag them into paying their new family homes tax.

“This is a tax on aspiration, on working hard and investing well, and Labour will stop at nothing to make as many people as possible liable for it.”

Sir James Cleverly, the Shadow Housing Secretary, described the inspections as “snooping”.

“Hard-working families and pensioners face the prospect of HMRC tax inspectors snooping around their gardens and inside their homes, to justify hiking taxes on them,” he said.

“Even homes which are below the new tax thresholds face these intrusive checks, with the threat of criminal prosecutions and fines if people refuse.”

Shadow Housing Secretary James Cleverly said the new inspections amounted to ‘snooping’

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HMRC’s Valuation Office will initially rely on third-party data and publicly available information to assess property values.

Satellite technology will also be used to “spy” on homes targeted under the surcharge.

Ministers have confirmed in parliamentary questions that “internal inspections” of homes will also be carried out.

Inspectors will record details including a property’s size, architectural style, number of floors, rooms, bedrooms and bathrooms.

Jonathan Russell, the Valuation Office’s chief executive, told MPs earlier this year that homes previously valued above £1.5million would be reassessed to check whether they now surpassed the £2million threshold.

He said he wanted to “make sure we’re not missing anything.”

Ministers have confirmed in parliamentary questions that ‘internal inspections’ of homes will also be carried out

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Property experts have told the Government that “regular” inspections by qualified surveyors conducting full physical surveys would be needed to keep valuation records up-to-date.

A Government spokesman defended the policy by pointing to “inequality” in the council tax system.

“The public understands that we are addressing a longstanding unfairness, where a Band D home in Darlington pays more in council tax than a £10m mansion in Mayfair,” the spokesman said.

“The Valuation Office has extensive experience valuing domestic property, and will use a wide range of evidence to determine bandings.”

The spokesman claimed any visits would take place by prior agreement with the property owner and in line with the Government’s code of practice.

Junior Treasury minister Dan Tomlinson, meanwhile, confirmed the Valuation Office would contact homeowners to “arrange a visit.”