Queen's 100th birthday messages may have risen by 50% in 10 years
The number of congratulatory messages sent by the Queen to people reaching their 100th birthday may have risen by up to a half over the past decade.
An estimated 5,780 people living in the UK were 100 years old in the middle of 2015, according to the Office for National Statistics (ONS).
This compares with 3,710 at the same point in 2005 - a jump of 56%.
When people are approaching 100, it is traditional for their family to apply for a free birthday message to be sent from the Queen.
The figures also show that the total number of people aged 100 and over rose almost two-thirds in the past decade, from 8,850 in 2005 to 14,570 in 2015.
This suggests around one in 5,000 people in the UK was aged 100 or over last year.
ONS statistician Pamela Cobb said: "Although the majority of the very old are women the number of men reaching the oldest ages is increasing as male mortality improves."
The figures reflect the UK's ageing population. In the past three decades, the number of people aged 100 and over quadrupled in number, while those aged 90 and over almost trebled.
There were more than half a million people aged 90 and over in Britain last year - seven in 10 of them female.
ONS statistician Angele Storey said: "The main driver of population ageing in the UK in recent decades has been improving mortality at all ages but particularly at older ages.
"This has contributed to increasing numbers of people reaching ages 90 and above. The large peak in fertility in the 1960s ' the baby boomers' will contribute to future population ageing."
Jane Ashcroft CBE, chief executive of Anchor, a charity and care home provider, said people should "celebrate that we're living longer".
She added: "Every day I see first-hand that old age is a time for living and our residents are a constant source of inspiration for us, living life to the fullest no matter their age.
"We just need to make sure that we listen and take care of this important and growing section of society."
Other findings in the ONS report include.
:: There were around 850 people aged 105 or more in 2015, double the number a decade previously. Nine in 10 were female.
:: Those aged 90 and over made up just 0.9% of the total UK population in 2015, but the size of the group relative to the population is rising.
:: Of those aged 90 and over, around four in five were estimated to be below 95.
:: In 1985 the median age in the UK was 35.4 but in 2015 it had risen to 40.
:: At birth, life expectancy is 82.8 years for females and 79.1 years for males.