Labour have accused Boris Johnson’s ethics adviser of giving “carte blanche” to rule breaking at the top of government after he allowed the health secretary to keep his job despite breaking the ministerial code.

Lord Geidt, the independent adviser on ministerial standards, found Matt Hancock guilty of a “technical” breach of the rules after he failed to declare his sister’s company, in which he holds shares, had become an approved contractor for the health service.

But he described the issue as “minor” and did not recommend Mr Hancock resign.

Traditionally, ministers have stood down if they have been found to have breached the code, which is designed to police their behaviour.

Labour’s deputy Labour leader Angela Rayner has now written to Lord Geidt to warn that his decision sets a “concerning precedent”.

Ms Rayner said she had asked Lord Geidt whether he agrees that his decision “sends a very clear message that the rules don’t apply to cabinet ministers”.

The case will damage public trust in politics and give “carte blanche to other ministers to break the ministerial code safe in the knowledge that they will not face sanctions,” she added.

Mr Hancock faced calls to resign after it emerged that he held shares in the firm, Topwood Limited, which specialises in the secure handling of documents.

He declared the shares in March this year.

But it later emerged that the company won a spot on a ‘framework’ to provide services to the English NHS in 2019, as well as contracts with the NHS in Wales.

Mr Hancock became health secretary in July 2018.

Lord Geidt, who was appointed by Boris Johnson, found in a much-delayed report released last week that the company’s approved contractor status could be seen to “represent a conflict of interest” and should have been declared.

But he added of Mr Hancock: “I assess this earlier failure to declare the interest was as a result of his lack of knowledge and in no way deliberate, and therefore, in technical terms, a minor breach of the ministerial code.”

Ms Rayner said it was “simply not believable or reasonable” that Mr Hancock “didn’t know about this conflict of interest”.

She accused Lord Geidt of allowing Mr Hancock to use a “completely ridiculous excuse” to keep his position at the top of Government.