UK Brexit officials have admitted breaching strict data rules after sharing private information handed to them by the SNP with a Scottish Tory politician.

Keith Brown, the SNP’s deputy leader, submitted a complaint after his office received a call from Scottish Tory MP Luke Graham which set alarm bells ringing.

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Mr Brown has now written to the head of the Civil Service, Mark Sedwill, asking him to investigate whether such breaches are widespread.

He insisted it was a “deeply concerning incident which should never have occurred”.

The row started after Mr Brown, who represents Clackmannanshire and Dunblane, wrote to junior Brexit minister Robin Walker with concerns raised by a constituent who owns a business relying on EU workers.

Mr Brown’s office then received a call from Mr Graham’s staff asking for more details – despite never sharing the case with the Scottish Tory MP.

Claire Moriarty, permanent secretary of the Department for Exiting the European Union, has now confirmed there was “an unauthorised disclosure of information by a member of staff”.

In a letter to Mr Brown, she said: “My officials have written to Luke Graham MP to ensure that the communication related to this matter is deleted from his records.

“I would like to reassure you that appropriate action has been taken in line with our security, data protection and disciplinary policies, as well as mandatory staff training.”

Mr Brown said: “Constituents raise concerns with their MSPs in complete confidence. It is unacceptable for strict data protection rules to be cast aside for political gain – which appears to have been the motivation here.”

He added: “Just how widespread are these practices? Are Tory ministers regularly divulging confidential information to Tory MPs for political expediency?

“And why are Tory MPs getting priority over SNP members raising legitimate concerns on behalf of their constituents? Are UK minister operating a dual speed system which treats MSPs as second class?

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“It demonstrates that the whole Westminster system is completely broken – and that goes right to the heart of the department that is supposed to be handling Brexit.”

Mr Graham said he was “informed that there was a constituent issue that may have not been responded to, but received no personal constituent data”.

He said: “My office called Keith Brown’s office to confirm details about the issue and ask if his office would give further details about the case so we could support.

“My office has a strong record of working with all levels of government to resolve constituent issues/concerns and my team and I will continue to do so.

“It is also standard practice to include the local MP in any correspondence referencing that MP’s office. I received no such correspondence from Mr Brown or his team.”