The population of the UK has risen by its lowest rate for over a decade, the first official population estimates since the EU referendum show.

Demographers’ latest calculations show there were an estimated 66,040,229 million people living in the country at the end of June last year.

Over the 12 months to the middle of 2017, the number of inhabitants increased by 392,000 people – or 0.6%, the lowest growth rate since mid-2004.

The Office for National Statistics (ONS) said the EU referendum is likely to be one of the key drivers of the changes.

The Migration Statistics Quarterly Bulletin for the period noted that: “The number of people immigrating for a definite job has remained stable but there has been a 43% decrease in the number of people immigrating to look for work over the last year, especially for EU citizens.

“These changes suggest that Brexit is likely to be a factor in people’s decision to move to or from the UK – but decisions to migrate are complex and other factors are also going to be influencing the figures.”

The ONS figures come in contrast to last year’s, when the UK saw its sharpest annual population increase since 1948 with a rise of 538,000.

While the rate of population growth in the year to mid-2017 was slower than in recent years, it remains above that seen in the period before 2004.

The slowed-down pace of immigration was described as “significant” and one of the two key drivers of the rate of population growth, accounting for 59% of change.

ONS figures from earlier this year showed net migration to the UK from the EU in the year to September 2017 fell below 100,000 for the first time in more than four years (90,000) – down from an estimated 165,000 in the previous year, and a fall of 45%.

Natural change – the number of births minus the number of deaths – of 159,800 accounted for just under half (41%) of the overall increase.

Around two-fifths of local authority areas showed negative natural change, reflecting older age structures, and mostly in rural and coastal areas.

Neil Park, ONS head of population estimates unit, said: “This is the lowest annual population growth since 2004 due to a fall in net migration, fewer births and more deaths than previously seen.

“The effect is most pronounced in London and other areas that have seen high levels of immigration in recent years.

“Nevertheless, the population is still growing faster than at any time since the post-war ‘baby boom’ and the expansion of the EU in 2004.”

The figures showed the proportion of the population aged 65 and over reached 18.2% in mid-2017, up 0.2%.

Two-thirds of local authorities (259) saw a slower population growth rate in the year to June 2017 compared with the previous 12 months.

While many authorities with decreasing populations in mid-2017 are on the north and west coasts of Scotland or the coast of Cumbria, many other local authorities also had decreasing populations, the ONS said.

A total of 346 local authority areas saw a population increase in the year to June 2017, compared with 366 areas the previous year.

Robin Maynard, director of charity Population Matters, said: “This year’s reduction in rate of growth is welcome but it’s the result of circumstances, not leadership.

“The Government should not be a passive spectator to population growth. If we want a better quality of life and a healthy natural environment in this country, we can’t continue to treat population growth as an inevitability we have to accommodate, instead of a challenge we must and can meet – through compassionate, available means and positive action.

“The Government needs to have a strategy to achieve a sustainable population in the UK. It needs to put a minister in charge, identify the effective solutions, create a rational, integrated policy and implement it.”