Led by Jemima Khan, the ex-wife of Pakistani cricketer-turned-politician Imran Khan, the demonstrators chanted slogans and waved banners, calling Pakistani president General Pervez Musharraf a "butcher" and a "terrorist".

Pakistani lawyers, students and journalists turned out for the protest, which was organised by a disparate group of political parties and human rights groups.

Hina Jilani, a Supreme Court lawyer, said: "We want to show everyone inside Downing Street that every section of Pakistani society is now opposed to Musharraf.

"My message to Gordon Brown is that he must not allow Pakistan to go the way of Zimbabwe - Pakistan must be supported so we can save our country. If not, Pakistan will never recover from the damage Musharraf has inflicted."

The demonstration was organised to encourage the British government to put more pressure on Musharraf's military regime.

President Musharraf declared emergency rule last Saturday, claiming it was necessary because of threats against the nation.

Since then, thousands of people including lawyers and activists from opposition parties, have been arrested.

The scale of arrests has led critics to claim General Musharraf only declared the state of emergency to keep hold of power.

Imran Khan, along with several other leading politicians, has been under house arrest following the announcement of the state of emergency.