Donald Douglas Stewart-Whyte and Mohammed Usman Saddique were charged with intending to commit acts of terrorism, police said on Wednesday.

The men are accused specifically of planning to "smuggle the component parts of improvised explosive devices onto aircraft and assemble and detonate them on board."

Stewart-Whyte, a native British convert to Islam, is also charged with possessing illegal firearms.

Both men will appear in court on Thursday.

Three other men were released without charge on Wednesday after being held for 28 days - the maximum suspects can be detained without charge under British anti-terrorism laws.

25 people were arrested on August 10 over what police said was a foiled plan to use homemade liquid explosives to bring down several airliners on the way from Britain to the United States.

A total of 17 people have been charged in connection with the alleged plot.