Michael D Higgins and Micheál Martin in London ahead of Queen Elizabeth’s funeral

They will later both be hosted at Buckingham Palace by King Charles III at a reception for world leaders flying in for the solemn State funeral tomorrow.

The Head of State’s attendance at Westminster Hall is seen as a personal expression of gratitude, after the Queen hosted President Higgins on a first-ever Irish State visit to the United Kingdom in 2014.

The four-day visit, which came three years after the Queen’s historic visit to Ireland in 2011, saw the Queen host a glittering white-tie banquet at Windsor Castle — where the monarch will be laid to rest in St George’s Chapel tomorrow, alongside her late husband, Prince Philip.

Meanwhile Mr Martin will also file past the coffin surmounted by the Royal Standard in central London, before a meeting with new British Prime Minister Liz Truss at 10 Downing Street.

The pair are scheduled to have talks for a full 45 minutes, which will certainly deal with the Northern Ireland protocol issue once expressions of sympathy and condolence are out of the way.

But for reasons of respect in advance of the State Funeral for Queen Elizabeth tomorrow there will be no joint communiqué or even a press briefing on the topics touched upon.

The meeting is being described as private.

The President and Taoiseach will both attend tomorrow’s funeral for the 70-year monarch, whose reign was the longest in British and western history, ten years longer than that of Queen Victoria.

Later today they will sign a Book of Condolence at the Foreign and Commonwealth Office headquarters in Lancaster House, where an agreement was famously signed to establish the democratic and independent state of Zimbabwe.

The Irish Heads of State and Government have two of the coveted places in Westminster Abbey, as politicians and potentates from around the world descend upon the English capital for Queen Elizabeth II’s final requiem.

It is highly unusual for the President and the Taoiseach to both be absent from Ireland at the same time.

But the close ties between these islands have demanded a full formal attendance for the first time in the history of this State.

The Irish Embassy in London has been facilitating the arrangements, with security provided by the Metropolitan Police.

The walk-though at Westminster Hall may been viewed on the live broadcast feed of the lying-in-state. The two men will make separate visits, it is understood — with the British public continuing to simultaneously stream past the coffin of Her Majesty. It is understood that this will take place at around 11.40am today.

Mr Martin will have no direct engagements with other world leaders at or after the funeral tomorrow, although there may be an opportunity for a quick word with such as US President Joe Biden.

Later this week the Taoiseach flies to New York on a two-day visit for the United Nations General Assembly.

A Government spokesman told the Irish Independent: “The President will attend first, followed by the Taoiseach.”

He added that their spouses — Sabina Higgins and Mary O'Shea — would both later also be appending their signatures to the Book of Condolence.