Theresa May's aim to reduce net migration to below 100,000 has suffered a setback, with the latest data showing the figure increased 23,000 to 176,000 last year.

The reversal of recent declines suggests that the home secretary's drive to hit the Conservative migration target by the 2015 general election is stalling.

Office for National Statistics figures published on Thursday show a net flow of 176,000 long-term migrants into Britain in the year to December 2012. The number is well below the 215,000 for 2011 but above the 153,000 for the 12 months to October 2012.

The ONS said the quarterly increase in net migration – the estimate of those coming to live in Britain for more than 12 months minus those leaving to live abroad for more than 12 months – suggests the decline seen quarter by quarter since June 2011 has not continued.

Official statisticians said the increase was a result of fewer people leaving the country to live abroad rather than any rise in the level of immigration.

The raw data shows 497,000 people came to live in Britain in the year to December 2012, while 321,000 left to live abroad. The emigration figure is 30,000 lower than the year before.

The latest Home Office visa figures show the squeeze on overseas students coming to Britain has continued, with 180,000 arriving in Britain to study in 2012.

They show that in the 12 months to this June, 204,000 study visas were issued, 5% fewer than the previous year. This includes a 54% drop in study visa applicants from Pakistan and a 35% fall from India.

While visa applications to universities have risen 4%, those to further education colleges have fallen 25% and those to English language schools are down by 16% over the latest period.

The visa figures also confirm a second squeeze on family migration, with a 24% fall in family-related visas to 34,201 issued in the 12 months to June. The largest fall was in family visas issued to US citizens to join British husbands or wives,down by 46% to 1,242. Family visas issued to Nepalese applicants are down 37% and those to Pakistanis down 14%.

The ONS said there had been a "statistically significant" fall in the net migration of non-European Union citizens – 157,000 in the year ending December 2012 from 204,000 the previous year. This was driven by a drop in immigration, particularly in the number of citizens of New Commonwealth countries, which includes African nations such as Botswana, Kenya and Malawi, and Indian subcontinent countries such as Bangladesh, India and Pakistan.

The Home Office figures also show that enforced removals of illegal migrants from Britain have fallen by 7% to 14,602 in the past year, while the number of voluntary departures was little changed at 29,265. This may explain the motivation behind the Home Office's much criticised "go home or face arrest" mobile van advertising campaign.

The ONS migration figures include a new estimate for the foreign-born population in Britain, a figure often quoted in the immigration debate. They show that of the 7.6 million people – 12% of the resident population – who were born abroad, 3.1 million are British citizens who have lived in the country long enough to become citizens or who were born abroad to British parents.

India was the most common foreign country of birth in 2012, with 729,000 UK residents born in India, while Polish was the most common non-British nationality, accounting for 700,000 UK residents. Countries that joined the EU in 2004, including Poland, the Czech Republic and Lithuania, accounted for 53,000 arrivals, down from 77,000 the previous year.

The ONS revealed a quarter of births – 25.9% – in 2012 were to mothers born outside the UK, a slight increase from 25.5% in 2011. Poland remains the most common country of birth for non-UK born mothers in 2012, while Romania moved into the top 10 most common countries of birth for non-UK born mothers in 2012, replacing China.

Sarah Mulley, of the Institute for Public Policy Research, said the government was running out of options to meet its 100,000 net migration target by 2015: "Recent declines have been driven in large part by falling numbers of international students, which has come at a high economic cost, but this trend appears to be levelling off.

"The government cannot further reduce student numbers without imposing even more significant costs on the education sector and the UK economy.

"Indeed, the Department for Business, Innovation and Skills has stated its ambition to attract an additional 90,000 international students to the UK by 2018, recognising the importance of the education sector to growth and exports.

"The government's focus on net migration statistics is at risk of obscuring more important questions about immigration. They should be more focused on how new migrants can be integrated into communities and how the UK can attract the skilled migrants it needs."

The immigration minister, Mark Harper, said the government's drive was working:"Net migration is down by a third since its peak in 2010. Our reforms are working and are building an immigration system that works in the national interest. We have tightened immigration routes where abuse was rife, but are still encouraging the brightest and best to come here to study and work.

"We are committed to bringing net migration down from the hundreds of thousands to the tens of thousands. We are working across government to protect public services and ensure our welfare system is not open to abuse. The immigration bill, which will be introduced this year, will make it easier to remove people who have no right to be in this country."

Chris Bryant, shadow immigration minister, said: "The prime minister promised 'no ifs and no buts' to get net migration down to the tens of thousands by the end of the parliament. But these figures show an increase in immigration over the last three months, with more EU migrants arriving.

"This increase in net migration is a blow for Theresa May, exposing once again the government's empty rhetoric on immigration."