Amnesty International protestors, who will unfurl banners with the names of all 725 prisoners executed in the US since 1977, will voice their outrage at the USA's capital punishment record.

A giant 'grim reaper' will appear outside the embassy, a symbol of the scale of judicial killing in the USA in recent years.

An Amnesty International delegation will present a letter to the embassy calling on the president to impose an immediate moratorium on federal executions. He will be urged to show leadership and begin the process of moving his country away from the death penalty.

Amnesty International activists will also highlight the case of Napoleon Beazley (aged 24), due to be executed in Texas on 15 August for an offence committed when he was 17. The USA currently executes more juvenile offenders than any other country.

There will be an address to those assembled in Grosvenor Square by Maria Telesco, the noted American death row expert, a veteran anti-death penalty campaigner who protested at the execution of Ethel and Julius Rosenberg for espionage in 1953.