Several thousand people protested on Thursday outside the Indian embassy in London against the country's move to strip the Indian-controlled part of Kashmir of its autonomy.
The protesters held up signs reading "Kashmir is bleeding" and waved Kashmiri and Pakistani flags. Police separated them from a smaller pro-Indian counter-demonstration.
AFP reporters saw police making at least one arrest.
"Everybody has to stand up. This is a turning point," said Shazad Ahmed, a 36-year-old IT worker from the Pakistan-controlled part of Kashmir who attending the protest with his wife and two daughters.
Mohammed Beshir, 76, also from the Pakistani part of Kashmir, said: "We want the British people to intervene".
Kashmir is split between arch-rivals India and Pakistan.
The Indian-controlled parts of Kashmir have been in lockdown since August 4, with freedom of movement restricted and phones and the internet cut.
A day later, New Delhi scrapped Article 370 in the Indian constitution that granted Kashmir special autonomy.
The United Nations Security Council is scheduled to discuss the issue at a closed-door meeting on Friday.