Britain's population rose by 400,000 last year – the equivalent of adding a city the size of Coventry to the country.

The increase means the total is on course to reach 70million in eight years – two years earlier than previous predictions.

Immigration, which was higher in 2018 than in previous years, was the cause of much of the rise, the Office for National Statistics said.

The estimated population a year ago was 66,435,500, up by 0.6 per cent or 395,000 on the mid-point of 2017.

Net migration – the number arriving in the country minus those leaving – was 275,000. This was 45,000 higher than in 2017 and 6,000 higher than the average over the past five years. Meanwhile, there were fewer births and more deaths in 2018 than in the previous year.

Britain's population rose by 400,000 last year – the equivalent of adding a city the size of Coventry to the country. The Office for National Statistics (ONS) said the annual growth rate is still slower than any year since mid-2004

Neil Park of the ONS said: ‘For the fifth year in a row, net international migration was a bigger driver of population change than births and deaths.

‘However, overall population change to the year mid-2018 has remained fairly stable as an increase in net international migration has been roughly matched by the fewest births in over a decade and the highest number of deaths since the turn of the century.’

The breakdown from the ONS found that last year was the 36th in a row in which the population has risen.

The last period of contraction was in the 1970s and early 1980s, when the struggling economy led to low immigration and drove high numbers out of the country. Annual population growth was running at around 150,000 a year until 1998, before it started climbing sharply to a peak of more than 500,000 in 2016 – the year in which the referendum result led to lower immigration from Europe.

There were 626,000 immigrants in the 12 months to the middle of 2018, and 351,000 emigrants. Births fell by 2 per cent on 2017 to 744,000, and there was a 3 per cent increase in deaths to 623,000.

It added that on top of its immediate impact on population, migration affects the number of births and deaths.

Recent migrants tend to be younger and have more children than people already living in the UK, and in 2017 some 28.4 per cent of babies were born to mothers who were born abroad.

Despite the rising number of immigrants, the population generally continues to age.

The ranks of the over-65s swelled by 23 per cent to 10.6million in the decade to 2018, while there were 22.8 per cent more over-85s at 1.6million.

In comparison there were only 7.8 per cent more children – up to 12.6million – and 3.5 per cent more people of a working age.

Nearly all of the population increase was in England rather than Scotland, Wales or Northern Ireland.

The four local authorities with the fastest-growing population were all in central London – the City of London, Westminster, Camden and Tower Hamlets – as 237,300 people moved to the capital. This was mainly because of international migrants and young people looking for education and careers

However, an estimated 340,500 residents left the capital – mostly young families looking for better schools and lower crime and pollution levels.

Many are also being forced out by sky-high rents and house prices into cheaper areas in the commuter belt.

Lord Green of Deddington, chairman of Migration Watch UK, said: ‘These latest statistics underline the consequences of the Government’s failure to bring immigration under control and in line with their repeated promises and the strong wishes of the public.

‘The candidates for the Conservative leadership should be invited to say what they propose to do about it.’