A man arrested under the Terrorism Act after deliberately driving at police outside Queen Elizabeth II's Buckingham Palace residence in London had a "four-foot sword" in his car, police said on Saturday.

Upon being challenged by officers, the 26-year-old attacker "reached for what we now know to be a four-foot sword which was in the front passenger foot well," the police statement said.

"The man, who repeatedly shouted Allahu akbar (God is greatest), was incapacitated with CS spray".