The latest projections for the UK's population will be published.
Statisticians will today set out estimates of the future number and age structure of people living in the country.
They are based on the most recently available population estimates and a set of "underlying demographic assumptions" regarding births, mortality and migration.
The Office for National Statistics discloses the projections for the UK and its constituent countries every two years.
In the last set, published in November 2013, the total population was projected to rise by nearly 10 million over the next 25 years from an estimated 63.7 million in 2012 to 73.3 million in 2037.
Sixty per cent of this increase - or 5.8 million - was said to be due to migration, either directly through new arrivals into the country or indirectly through the impact on the birth rate.
The latest estimates are likely to spark fresh scrutiny of the issue of immigration.
In August it emerged that net migration to Britain - the difference between the number of people entering and leaving the country - reached a record high of 330,000 in the year to March.
It was also revealed at the same time that last year one in eight people living in the UK were born abroad after a "statistically significant" increase in foreign-born population.