Queen Elizabeth resting after first night in hospital in years

Britain's Queen Elizabeth, 95, spent a night in hospital for the first time in years for what Buckingham Palace termed "preliminary investigations", but was in good spirits and back at work at Windsor Castle.

The world's oldest and longest-reigning monarch cancelled an official trip to Northern Ireland on Wednesday. The palace said the queen had been told to rest by her medical staff, and that her ailment was not related to Covid-19.

"Following medical advice to rest for a few days, the queen attended hospital on Wednesday afternoon for some preliminary investigations, returning to Windsor Castle at lunchtime today, and remains in good spirits," the palace said late on Thursday.

The Palace gave no details on what had prompted the medical attention.

A royal source said the queen had stayed at the King Edward VII hospital in central London for practical reasons and that her medical team had taken a cautious approach.

Elizabeth, who is queen of 15 other realms including Australia, Canada and New Zealand, returned to her desk for work on Thursday afternoon and was undertaking some light duties, the source said.

Gillian Keegan, a junior health minister, said it was concerning to hear that the queen had stayed a night in hospital but that she appeared to be on the mend.

"She's just so fantastic and I hope that she's feeling better today," Keegan said.

Elizabeth, who acceded to the throne as Britain was shedding its imperial power, has symbolised stability for generations of British people, building the popularity of the monarchy despite seismic political, social and cultural changes that threatened to make it an anachronism.

A quiet and uncomplaining dedication to duty, even in old age, has earned her widespread respect in Britain and abroad, even from republicans who are eager for the monarchy to be abolished.