Prime Minister David Cameron was due to visit the scene of a colonial-era massacre Wednesday, reportedly to express regret for the gunning down of hundreds of unarmed Indian protesters by British troops in 1919.
He is on the last leg of a three-day trip aimed at forging deeper economic ties during which he has argued for a closer partnership between Britain and its former colony based on their shared history and common democratic values.
But the trip to the northwestern city of Amritsar, the home of the Sikh religion and scene of a massacre still taught in Indian school books, will see him tackle one of the enduring scars from British rule, which ended in 1947.
He is set to visit the holiest shrine for the Sikh religion, the Golden Temple, before travelling to Jallianwala Bagh, where British troops gunned down unarmed protesters on April 13, 1919, local and diplomatic sources told AFP.
The number of casualties at Jallianwala Bagh is a matter of dispute, with colonial era records showing it as several hundred while Indian figures put it at between 1,000 and 2,000.
The secretary of the memorial site, S.L. Mukherjee, told AFP: "I hope he pays homage and apologises for the killings."
Reports in British newspapers say he will stop short of an apology, but will leave a message of condolence in a visitor's book and express regret for the loss of life.
Bhusan Behl, who heads a trust for the families of victims of the massacre, has campaigned for decades on behalf of his grandfather who was killed at the entrance to the enclosed area.
He said he was hoping that Cameron would say sorry for the slaughter ordered by General Reginald Dyer, which was immortalised in Richard Attenborough's film "Gandhi" and features in Salman Rushdie's epic book "Midnight's Children".
The incident in which soldiers opened fire on men, women and children in Jallianwala Bagh garden, which was surrounded by buildings and had few exits, making escape difficult, is one of the most infamous of Britain's Indian rule.
"A sorry from a top leader would change the historical narrative and Indians will also feel that in some way they can forget the past and move on," Behl told AFP.
The move is seen as a gamble by Cameron, who is travelling with British-Indian parliamentarians, and could lead to calls for similar treatment from other former colonies or even other victims in India.
A source close to the delegation said some advisors had voiced serious reservations in advance about the trip, which was kept a secret until Wednesday morning.
In India, the move is likely to be broadly welcomed as an acknowledgement of previous crimes, but it also risks focusing attention on the past at a time when Cameron has been keen to stress the future potential of Indo-British ties.
Expressing regret, while stopping short of saying sorry, could also invite debate about why Britain is unable to make a full apology.
Cameron is not the only senior British public figure to visit Amritsar in recent memory.
In 1997, Prince Philip accompanied the Queen but stole the headlines when he reportedly commented that the Indian estimates for the death count during the massacre had been "vastly exaggerated".
Cameron has made several official apologies since becoming prime minister, saying sorry for the official handling of a football disaster at Hillsborough stadium in 1989 and 1972 killings in Northern Ireland known as "Bloody Sunday."
In 2006, former British prime minister Tony Blair expressed his "deep sorrow" for the slave trade in a move that was seen as stopping short of a full apology.