Andrew Motion and Sir Peter Maxwell Davies appear to have looked for inspiration to the 18th-century imperialist anthem Rule Britannia to celebrate the enduring nature of her reign.

Instead of ruling the waves, she continues to outlive them. The lyrics of The Golden Rule, revealed here in full for the first time, have waves crashing against the shore and woods shrinking but all the time “your constancy survives”.

The Queen will hear the new anthem when it receives its world debut in a service at St George’s Chapel, Windsor, next Sunday. “It is simply that the Queen is a constant while politics and the world itself are ever-changing,” Motion said.

The service is one of the few official celebrations of the Queen’s birth in 1926. This week she is holding a lunch for those born on the same day. The Department for Environment, Food and Rural Affairs is one of the few government ministries doing anything — and that is only to plant a tree on a nature reserve.

The official birthday in June will have more of a fun element with Buckingham Palace turning into a theme park with a party for 3,000 children. British embassies around the world will hold receptions.

The Queen has scaled back her future diary engagements, in keeping with a woman entering her ninth decade, and will spend more of her time at Windsor away from the hurly-burly of London.

Royal insiders say she is more interested in celebrating her 60th wedding anniversary next year and the diamond jubilee of her reign in 2012, the year Britain is host to the Olympics, than merely mark the passing of her own years.

The new work mirrors that of the poem Motion wrote to commemorate the golden jubilee in 2002. On that occasion he looked back at events of the first half-century of her reign while the Queen was praised for her constancy through change.

“It’s true that the golden jubilee was loitering in my mind,” said Motion, who has previously commemorated in poetry the Queen Mother’s 100th birthday, her death and Prince William’s 21st. “For this new work I didn’t want particularly to refer to her age of 80 as such.”

Maxwell Davies said: “Andrew and I met up last year and, yes, I think it was me who suggested that we look at the continuity of her reign and life.” He then asked Motion to write his words before he composed his music.

The full 20-minute version of The Golden Rule will be played with a chamber orchestra at Windsor in late September; Maxwell Davies is also working on another composition to be played at a BBC Proms concert in July to celebrate the Queen’s birthday.

This will be only the second time during her reign that the Queen has been to the Proms. She went first in her golden jubilee year of 2002, but gave the impression that she was not hugely fond of some of the music.

On her birthday on Friday, she and the Duke of Edinburgh will meet members of the public in an informal walkabout outside Windsor Castle. The Prince of Wales will then give a televised tribute to his mother before a dinner for the family at the newly restored Kew Palace in the evening.

When royal officials began planning for the Queen’s birthday, she told them she wanted a “low-key” family celebration and preferred them to concentrate their efforts on next year’s diamond wedding celebrations.

In diamond jubilee year, the Queen will be 86. Her mother lived to 101 and the Queen seems in remarkably good health, so it is conceivable she could break Queen Victoria’s record of 63 years on the throne. Victoria, who succeeded to the throne at the age of 18, was 81 when she died in 1901.

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