Liz Truss will meet King Charles III for the first time since the death of the Queen on Friday afternoon.
The prime minister is expected to go to Buckingham Palace for an audience with the King after his arrival in London from Scotland.
After his meeting with Truss, who has been in office for only four days, Charles is expected to give a televised address to the nation.
Truss is unlikely to make a speech on Friday but will give a reading at a service to commemorate the Queen at St Paul’s Cathedral, due to take place at 6pm on Friday.
Much government business has been suspended, but Truss started the day with a cabinet meeting where ministers paid tribute to the Queen and spoke of their recollections of meeting her, before observing a moment of silence.
She is later likely to hold calls with international leaders who wish to express sympathy with the British people.
Ministers have also met to discuss logistics for the national mourning period and the Queen’s funeral. These are largely a matter for the Palace, but the government will be involved in making arrangements for policing and deciding whether there will be a bank holiday to mark the funeral.
The government has released guidance saying there is no obligation on businesses or sporting and entertainment organisers to cancel events, although many are doing so already.
In Westminster, MPs observed a minute’s silence for the Queen and began making tributes to her in the House of Commons, which will continue on Saturday. Parliament is unlikely to sit next week out of respect for the Queen.
The Labour leader, Keir Starmer, also led tributes to the Queen at a meeting of the shadow cabinet on Friday morning, Labour said, with the meeting observing a minute of silence.
