The Treasury has refused to reveal when it first proposed its £30,000 charge on residents non-domiciled, amid claims that the government stole the policy from the Tory party.

Despite boasting in response to a similar request that it had been working on proposals for an overhaul of inheritance tax before the Tories had, the government turned down similar questions on the non-dom policies.

At their October party conference, the Tories outlined a £25,000 charge for non-doms to pay for raising the IHT threshold to £1m. Alistair Darling then announced IHT changes and a £30,000 charge for non-doms the next week.

‘You have asked for information on the timing of when particular stages in the formulation or development of a policy measure occurred, and the titles of documents. Our information is not recorded in that way as a readily available series of discreet information,’ the Treasury response to Accountancy Age’s Freedom of Information request said.

When The Daily Telegraph asked about the government’s IHT changes, it revealed it had been working on them as early as January, and published its response to the request on its website.

Tory shadow chief secretary to the treasury Philip Hammond said: ‘When it suited Gordon Brown, the Treasury responded to an FOI request on the origins of their Inheritance Tax policy with amazing speed. Those documents showed that the IHT idea was only advanced by government after the Conservatives raised it.

‘People will draw their own conclusions about where Labour got the non-doms idea from.’