Families of the dead soldiers have long argued the officers who ordered their execution failed to take into account the horrific circumstances of the 1914-1918 war that put soldiers under immense stress and may have affected them psychologically.

One soldier set to be pardoned, Private Harry Farr, was suffering from severe shellshock and had previously been hospitalised when he refused to return to the front line, his family has long maintained.

He was shot at dawn on October 2, 1916, aged 25.

Defence Secretary Des Browne said he had decided to grant a group pardon to more than 300 soldiers because the evidence did not exist to assess each case individually.

"I believe it is better to acknowledge that injustices were clearly done in some cases, even if we cannot say which - and to acknowledge that all these men were victims of war," Browne said in a statement.

Browne said he would seek parliamentary approval for the pardons as soon as possible.

Farr's granddaughter Janet Booth said the decision had come out of the blue and her 93-year-old mother was thrilled.

"She said she would like him to be pardoned in her lifetime," Booth told BBC radio.

Farr, a soldier with the 2nd Battalion Yorkshire Regiment, had already witnessed some of the horrors of the Second World War when he refused to return to battle and was ordered shot for cowardice.

"It was the sound of the gunfire that set his nerves off and he said 'I can't go on'," Booth said.

"He was shot at dawn but he refused a blindfold ... my grandmother always said he was no coward and that he was a sick man."

The British government said in March it would reconsider its initial refusal to pardon Farr after his family appealed. They contended his court martial was unfair because officers did not take shellshock into consideration.

"I am conscious of how the families of these men feel today. They have had to endure a stigma for decades," Browne said.

Of the approximately 300 British soldiers shot dead by their own side during World War One, 17 were executed for cowardice. Others were killed for deserting the army or disobeying orders.

However one military historian said the pardons were irrelevant as the executions were made in a different moral climate.

"It's pointless to give these pardons. What's the use of a posthumous pardon," Correlli Barnett told the Daily Telegraph.

"These decisions were taken in the heat of a war when the commanders' primary duty was to keep the army together and to keep it fighting."