Britain’s high commissioner to India laid a wreath on Saturday to commemorate the 100th anniversary of the Amritsar massacre, one of the worst atrocities of Britain’s colonial rule.

On 13 April 1919 British troops fired on hundreds of unarmed men, women and children in the northern town of Amritsar. Colonial-era records put the death toll at 379, but Indian figures say the number was closer to 1,000.

A hundred years later Britain has still made no official apology, and Dominic Asquith, the high commissioner, also failed to do so at the Jallianwala Bagh walled garden, where bullet marks are still visible. “You might want to rewrite history, but you can’t,” he said. “What you can do, as the Queen said, is to learn the lessons of history. We will never forget what happened here.”

In the memorial’s guest book Asquith, a descendant of Herbert Asquith, prime minister from 1908-16, called the events “shameful”.

“We deeply regret what happened and the suffering caused,” he wrote, echoing comments by the prime minister, Theresa May, in parliament on Wednesday, when she also stopped short of apologising.

About 10,000 unarmed men, women and children had gathered in the walled public garden in Amritsar to celebrate a spring festival that day. Many were angry about the arrest of two local leaders. Their detention had already sparked violent protests.

Brigadier General Reginald Edward Harry Dyer arrived with dozens of troops, sealed off the exit and without warning ordered the soldiers to open fire. Many local people tried to escape by scaling the high walls surrounding the garden. Others jumped into a deep, open well at the site as the troops fired.

“Heaps of dead bodies lay there, some on their backs and some with their faces upturned. A number of them were poor innocent children,” one witness later recalled.

Dyer said the firing had been ordered “to punish the Indians for disobedience”. Winston Churchill, then secretary of state for war, later called the decision “monstrous”.

Brig Gen Reginald Dyer ordered the attack ‘to punish Indian disobedience’. Photograph: Nehru memorial mueum

During a visit in 2013 the then prime minister, David Cameron, described what happened as “deeply shameful”, but stopped short of an apology.

In 1997 the Queen laid a wreath at the site, but her gaffe-prone husband Prince Philip stole the headlines by reportedly saying that the Indian estimates for the death count were “vastly exaggerated”.

On Wednesday, May told the House of Commons that the massacre was “a shameful scar on British Indian history”. “We deeply regret what happened and the suffering caused,” May said.

Amarinder Singh, chief minister of Punjab state, said May’s words were not enough. He said “an unequivocal official apology” is needed for the “monumental barbarity”. Indian newspapers also repeated calls for an apology. “Even in the centenary year of the massacre, Britain has refused to ... take that important step,” said the Hindustan Times.