The revenue department has admitted that it is possible for fraudsters to infiltrate its tax return system. In the past year alone HMRC said it had fended off about 17,000 attempts to make fraudulent or incorrect tax repayment claims worth nearly £100m.

The Sunday Times has reported today that many of the claims are not being stopped. One major firm of accountants admitted that 12 of its clients have recently been targeted.

One of the victims, Jackie Annesley, had her tax return hijacked by criminals who used it to steal more than £1,800 from HMRC in the form of a false claim for a tax repayment.

Three days before Christmas she was surprised to receive a letter from HMRC saying: “Thank you for your recent claim to repayment. A bank transfer for £1,826 is being made to your account.”

A few weeks later she received another letter from HMRC saying: “We have identified unusual activity on your self-assessment account which we suspect to be fraudulent.”

Annesley, who edits The Sunday Times Style section, said: “If the taxman is being hacked I cannot trust any bank or financial service.”

HMRC refused to say how many successful hacks there had been “for operational and legal reasons”. But it said that taxpayers’ login details were “like gold dust to fraudsters”.

More than 9m taxpayers filed an online return ahead of last Sunday’s deadline.

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