Boris Johnson’s proposed date for the Queen’s Speech would fall on the day the monarch usually departs for her festive break at Sandringham.
The Queen, 93, often travels to her Norfolk estate on the Thursday before Christmas, having hosted a family lunch for the royals at Buckingham Palace that week.
Downing Street said Mr Johnson would call for a Queen’s Speech to take place on Thursday December 19 with “reduced ceremonial elements” if he remains Prime Minister after the General Election.
A spokesman said: “Should this Prime Minister return, the State Opening of Parliament and the Queen’s Speech will follow on Thursday December 19.
“The state opening of Parliament will take place with reduced ceremonial elements, as was the case following the early general election in 2017.
“This is due both to the early General Election and the proximity of the state opening to Christmas.
“If there is a change of Government following the election it is anticipated that the Queen’s Speech would be in January on a more usual timetable, but this would be a matter for the incoming administration.”
The Queen does not usually return to London until after the February 6 anniversary of her accession, which she usually spends in private at Sandringham, reflecting on the anniversary of her father George VI’s death.
A Buckingham Palace spokesman said of the plans for a December 19 state opening: “It might impact minorly.”
It is thought that if the ceremony were to take place on December 19, it would be held in the morning, meaning the monarch, who would attend with the Prince of Wales, could leave for Sandringham in the afternoon if she chose to.
Reduced ceremonial elements would mean no crown, no robes and no carriages.
In 2017, the monarch wore a day dress and blue hat with yellow flowers, which sparked comparisons to the European flag, and arrived by car.
The pomp and ceremony of the event was scaled back because the date fell too close to Trooping the Colour.
The next Queen’s Speech will be the monarch’s 66th – and if it does happen to take place on December 19, will be just 66 days, or nine weeks and three days, after her last.
The state opening on October 14 was criticised for its timing, and came only 10 days before Mr Johnson made his successful call for the General Election to take place.
Former foreign secretary Dame Margaret Beckett branded it a sham, while Sir Ed Davey, deputy leader of the Liberal Democrats, accused Mr Johnson of being discourteous to the monarch.
Dame Margaret said at the time: “Everybody knows this is a sort of sham Queen’s Speech…We all know that what the Government wants is an election tomorrow.”