The new plan emerged as President Barack Obama said the US had played no role in Hong Kong's mass demonstrations.
The city's government has urged protesters to leave the main rally sites that have brought parts of Hong Kong to a standstill for more than six weeks, with police authorised Monday to back up bailiffs charged with clearing barricades.
Activists say they want to show their anger at Britain for not standing up to China over "breaches" of the agreement the two countries made before Hong Kong was handed back to China by Britain in 1997, designed to protect Hong Kong's social systems and way of life.
"They have the responsibility to make sure that the joint declaration has been implemented properly and that democracy and the high degree of autonomy of Hong Kong has been protected," Choi said.
She said she hopes for a turnout of hundreds and "maybe even thousands".
The group is a new offshoot of the protest movement, Choi added, with around 10 organisers from all walks of life including a secondary school student.
But Beijing has refused to back down on its insistence that candidates must be vetted by a loyalist committee.
Bailiffs are expected to start a clearout operation in the next few days, with thousands of officers put on standby over the weekend, according to local media.
But seemingly undaunted, activists have put up large posters around the protest areas announcing the consulate occupation on November 21 and a Facebook page for the event has more than 700 likes.
The British consulate said they had no comment.
