It’s been called Canada’s birth certificate and is considered one of the country’s most important founding documents.

But the British North America Act, signed in 1867, remains under lock and key in the United Kingdom, where the government charges more than $350 for visitors to take a peek.

Ironically, the paperwork that transformed Canada from a British colony to a federal dominion is still legally owned by the U.K., and the Canadian government has no immediate plans to retrieve it.

But, as Canada celebrates its 150th birthday, some say the time is right for the BNA Act to move across the Atlantic.

“It's that document that allowed my family to come to Canada, and it's that document that's given me such pride,” Lori Abittan told CTV News.

It’s believed that parts of the act were drafted in Highclere Castle, the same Victorian country house where the popular British television show “Downton Abbey” was filmed.

The picturesque estate was once home to Lord Carnarvon, the minister in charge of British colonies. Carnarvon helped write the act and worked closely with Canada’s founding fathers, including Sir John A. Macdonald, in planning Canada’s creation.

“They were sitting here during the conversations constructing these tricky clauses and the balance within it,” explained Lady Fiona Carnarvon, the modern-day lady of the house, as she took CTV’s Daniele Hamamdjian for a tour.

While Canada has no immediate plans to retrieve the historic paperwork, other countries have taken back their founding documents -- sometimes without permission.

In 1990, Australia borrowed its founding document from the U.K. to celebrate an anniversary. Prime Minister Bob Hawke later refused to give it back to Britain, and it has remained Down Under ever since.

For legal experts, keeping the BNA Act in Canada would carry symbolic significance.

“It survived, it's been amended, it's been interpreted. It has been, still, the bedrock of our legal system,” said former Supreme Court Justice Frank Iacobucci.

With a report from CTV’s Daniele Hamamdjian at Highclere Castle