Besides paying tribute to the 96-year-old queen, Britain's longest-reigning monarch, at Westminster Abbey on Monday, he also attended a reception for representatives from various nations hosted by King Charles III at Buckingham Palace on Sunday night and another by Secretary of State for Foreign, Commonwealth and Development Affairs James Cleverly.
He also met Charles and several new British cabinet members.
He conveyed the deep condolences of the senior Vietnamese leadership to Charles, other members of the royal family and the government and people of the U.K.
He highlighted Queen Elizabeth's role in the U.K.'s development and status, and her valuable support to Vietnam-U.K. cooperation.
He also held meetings with a number of foreign leaders who were attending the funeral.
More than 2,000 guests, including 500 world leaders, royal family members and officials representing nearly 200 countries and territories, attended the funeral.
The queen was crowned in 1952 at the age of 25 after the death of her father, King George VI.
Vietnam established diplomatic relations with Britain in 1973, and upgraded it to a strategic partnership in 2010.