LONDON (Reuters) - U.S. President Donald Trump was shown a handwritten parchment copy of the U.S. Declaration of Independence - one of only two known to exist - during a visit to British Prime Minister Theresa May’s office on Tuesday.

Trump, on a three-day state visit to London with his wife Melania, viewed the document with May and her husband Philip ahead of talks at her Downing Street residence.

The manuscript, known as the Sussex Declaration, is one of only two known handwritten parchment copies of America’s formative text.

It had been stored for more than 60 years in a strong-room among miles of documents in the West Sussex Record Office in southern England, until its significance was revealed by two Harvard University researchers last year.

May’s office said they hoped arrangements could be made for the document to form part of commemorations in 2026 marking 250 years since the Declaration of Independence. This could include its loan to the United States, they said.

Measuring 24 by 30 inches (60 by 76 cm), the Sussex Declaration is thought to date to the 1780s and most likely was written in New York or Philadelphia.

While other copies and printed versions of the Declaration exist, the only other ceremonial parchment is the Matlack Declaration, which dates from 1776 and is kept at the National Archives in Washington.