Tensions have heightened between India and Pakistan after New Delhi revoked the special status for Jammu and Kashmir last week.
As part of the appeal, overseas Pakistanis were requested to hold protests outside Indian embassies in their respective countries to show solidarity with the people of "Indian occupied Kashmir", Geo News reported.
A spokesman of Scotland Yard said they were aware of the planned protest on August 15 and had policing arrangements in place.
Geo News, citing intelligence reports, suggested that "the number of protesters will be in thousands - making it the biggest ever protest against India in Britain" - but the police refused to discuss the number of police on duty.
The protest will be joined by diaspora communities from all political parties, uniting them rarely for the issue of Kashmir, said the report. Two pro-Khalistan Sikh groups and secular Indian organisations will also be in attendance at the protest.
In a statement, Imran Khan's adviser, who will be himself attending the protest, said "it was moral obligation of all to speak up for the Kashmiri brothers and sisters, who were living in difficult circumstances".
According to the report, pro-Modi Indian groups had initially announced to hold a counter demonstration but changed their plans "after realizing that pro-Kashmir protesters will be huge in numbers and things could spiral out of control".
Dozens of Kashmiri and Pakistani groups have announced to attend the protest outside the Indian High Commission, near the London High Court, said the report.
Kashmir groups from Birmingham, Luton, Bradford, Manchester and Nottingham will also participate in the protest.
( With inputs from IANS )