AMRITSAR: British PM David Cameron on Wednesday described the 1919 Jallianwala Bagh massacre in Amritsar as "a deeply shameful event in British history", becoming the first serving prime minister to voice regret about one of the British Empire's bloodiest episodes in India.

He, however, just fell short of an apology but made clear that he considered the episode a stain on Britain's history that needed to be regretted by a democratically elected government of the UK.

"This was a deeply shameful event in British history - one that Winston Churchill rightly described at that time as monstrous" the left-handed Cameron wrote in the visitor's notebook at the massacre site.

His note further read: "We must never forget what happened here", underlining the word never twice.

"And in remembering we must ensure that the UK stands up for the right of peaceful protest around the world" it said.

The gesture came on the third and final day of his visit to India aimed at drumming up trade and investment.

Just minutes before he wrote the telling remarks, he told a few journalists: "it was a terrible act".

He also laid a wreath on the memorial site and then gently walked towards the table where visitor's notebook was kept.

His remarks are likely to be seen as an attempt to improve relations with India and to woo around 1.5 million British voters of Indian origin ahead of a 2015 election.

Cameron's visit has been largely focused on trade and investment so far.