Boris Johnson has been hit with a ministerial resignation as Tory anger over the behaviour of the Prime Minister's senior adviser Dominic Cummings boiled over.

Douglas Ross, the parliamentary under-secretary of state for Scotland, said on Tuesday that he was quitting after hearing Mr Cummings' efforts to defend his trip from London to Durham.

The first resignation over the allegations rocking the Government came as Cabinet Office Minister Michael Gove sought to defend his longstanding ally as having acted in an "entirely reasonable" way, and within the law.

But Mr Ross, the MP for Moray, said that "while the intentions may have been well-meaning", Mr Cummings' interpretation of the rules was "not shared by the vast majority of people".

"I have constituents who didn't get to say goodbye to loved ones; families who could not mourn together; people who didn't visit sick relatives because they followed the guidance of the Government," the Tory MP for Moray wrote.

"I cannot in good faith tell them they were all wrong and one senior adviser to the Government was right."

A No 10 spokesman said Mr Johnson "regrets" Mr Ross's decision to quit.

The resignation came amid continued concerns over how the Prime Minister's defence of Mr Cummings will affect the public, police and health workers during the pandemic.

In an extraordinary press conference for an adviser, Mr Cummings argued that his journey to Durham in March was justified as he sought to protect his family's health.

But many questions remained unanswered, including over his subsequent drive to Barnard Castle which he said was to test his eyesight after it was affected by Covid-19.

Mr Gove said the journey, some 25 miles from where the aide was isolating, was "completely appropriate" because he was "preparing to return to work" by checking he was safe to drive the long trip back to London.

"It'd have been entirely within his right to return to work that day on the basis of the advice he had been given, that's my understanding, so that drive was completely appropriate," Mr Gove told BBC Radio 4's Today.

Former Greater Manchester Police chief constable Sir Peter Fahy said officers had become "frustrated" by the fiasco, which may hinder policing with the rules "now very confused".

And he suggested that Mr Cummings' trip to Barnard Castle "certainly appears to be against the Highway Code - it's not the way to test your eyesight, and put potentially other people in danger".

He also said "it may well be that absolutely he'd have been turned back" by officers if they stopped him during the drive north from London in March.

NHS Confederation chief executive Niall Dickson said: "Because of the way this story has unfolded, there is certainly concern among our members, health leaders, that it could damage staff and public confidence in official guidance."