The population of Britain is to increase by almost 10 million in the next 25 years, with net migration accounting for more than half that number.

Projections released by the Office for National Statistics showed the UK population is expected to reach 74.3 million by 2039, up from an estimated 64.6 million in imd-2014.

The figures, only released once every two years, suggest 51 per cent of that increase will be as a result of people coming to the country from around the world. The rest was as a result of natural increase - a greater birth rate than death rate.

The ONS said the population was rising faster than when it made its last projection in 2012. It said there were expected to be 69 million people in Britain by 2024 - 250,000 more than was belived two years ago.

And if the indirect impact of people arriving in the next 25 years having babies of their own is taken into account, net migrations will account for more than two thirds (68 per cent) of the population increase to 2039.

The ONS also revealed the extent to which Britain will be made up of an increasingly ageing population over the next two and a half decades.

It said that the number of over-75s in the country will rise to almost 10 million from 5.5 million today, while by mid-2039 more than one in twelve of the population is projected to be aged 80 or over.

Statisticians said this had major implications "for the affordibility of pensions". It said that while in 2014 there are 310 people of retirement age for every 1,000 people of working age, by 2039 there would be 370 for every 1,000 - increasing the burden on workers via national insurance and taxes.