Britain's Queen Elizabeth leaves the annual Easter Sunday service at St George's Chapel at Windsor Castle in Windsor, Britain, April 1, 2018. REUTERS/Simon Dawson

LONDON (Reuters) - Britain’s Prime Minister Theresa May is to pay tribute to Queen Elizabeth for leading the Commonwealth with “service, dedication and constancy” as she thanks her for opening her homes to welcome leaders from across the world this week.

Queen Elizabeth has served as the head of the 53-country network of mostly former British colonies since she acceded to the throne in 1952. She is the monarch of 15 Commonwealth countries in addition to Britain.

On Thursday up to 47 leaders will gather at Buckingham Palace, one of the queen’s homes, where May will thank the Queen.

“This week you have opened your homes to us – here in London and in Windsor. Over many years you have been the Commonwealth’s most steadfast and fervent champion,” May will say, according to pre-released extracts of her comments.

“You have been true to the deepest values of the Commonwealth – that the voice of the smallest member country is worth precisely as much as that of the largest; that the wealthiest and the most vulnerable stand shoulder to shoulder.”

May is bidding to reinvigorate the organization as Britain seeks to define its post-Brexit role in the world, hoping that the Commonwealth will be one source of deeper trade ties.

May’s office said the tribute to the queen would come before a series of meetings between Commonwealth leaders to discuss the organization’s most pressing issues.