War veterans are expected to protest at the decision to give Britain's highest order of chivalry to the Japanese Emperor before their demands for compensation over alleged war crimes have been met.
But Buckingham Palace said that the Queen had acted on the advice of the Prime Minister and the Foreign Secretary, Robin Cook.
Downing Street confirmed that Tony Blair had been consulted, but pointed out that the decision to bestow the honour was "in the gift" of the Queen.
The present Emperor's father, Hirohito, was given the Order of the Garter before the Second World War, but had it stripped from him in 1941 after the attack on Pearl Harbour.
The honour, normally limited to only 24 members, was restored to Emperor Hirohito by the Queen during his state visit in 1971 and the Palace clearly believes the restoration of the honour to his son will provoke a limited response.
"It is in the Queen's gift but the Palace has had informal advice from the Prime Minister and the Foreign Secretary," said a Downing Street source. "Other Japanese emperors have been given the Order of the Garter.
Buckingham Palace said the Emperor would be bestowed with the Order of the Garter during the state visit from 26 to 29 May.
Ordinary members of the Order include Baroness Thatcher, Lord Callaghan, and Lord Hailsham. Other foreign heads of state who have the Order include the kings of Sweden and Spain, the Queens of Denmark and The Netherlands, and the Grand Duke of Luxembourg.