The government's attempts to reduce net migration to Britain to "tens of thousands" have suffered a fresh blow, with official data showing that the figure reached 252,000 last year, the highest calendar-year total on record.

The Office for National Statistics said the rise in net migration was driven by further falls in the level of emigration, with the number of British people going to live abroad now at its lowest level since 1998.

Immigration remained steady in the 12 months to March 2011, with 591,000 arrivals. A fall in the number of people coming to Britain to work was matched by a rise in the number of overseas students, particularly from China.

Home Office figures also published on Thursday show that the number of people turned away at British ports and airports this summer was 13% down on the same period in 2010, despite the pilot scheme that focused on passport checks for "high-risk" passengers and routes.

In the year to September 2011, a total of 17,399 were stopped, compared with 19,951 the previous year.

The data also shows a growing problem over the removal and deportation of failed asylum seekers and other illegal entrants. Removals and voluntary departures fell by 13%, to 13,253 in July to September this year, compared with 15,261 in the same period in 2010. That was the second lowest quarterly figure for 10 years. The number of foreign national prisoners sent home also continued to decline.

Asylum applications rose this summer, to 4,912, the highest level for two years, with the increase attributed to refugee claims from Pakistan, Iran and Syria.

The only crumb of comfort for Home Office ministers is that in the 12 months to March 2011, net migration dipped to 245,000, compared with the January to December figure of 252,000.

But it was too early to say whether this downward trend would continue, or whether it reflected a seasonal pattern in migration flows to and from Britain. The 245,000 total was 23,000 higher than the previous year.

The immigration minister, Damian Green, preferred to focus on these latest figures, which he said showed a fall in the number of student and work visas compared with a year previously. "They are an early sign that our policies are starting to take effect," he said, adding that the net migration figures were encouraging because they showed a fall "from the recent peak in September 2010".

He said new curbs would help bring net migration down to "tens of thousands over the course of this parliament".

Detailed net figures show that, at 336,000 people, emigration from Britain in the 12 months to March 2011 was at its lowest level since 2001.

The ONS said that 174,000 people left Britain to work abroad in the 12 months to March 2011 – the lowest number for five years, and down from the 203,000 in the 12 months to March 2010.

Australia, France, Spain and the US were the most popular destinations for British citizens going to live abroad, while Poland proved the most frequent destination for non-British citizens returning home.

Taking the 12 months to December 2010, immigration stood at 582,000, similar to 2004 levels. But within this total, ONS data confirmed that studying was the most common reason for migration to Britain; students overtook those coming to work.

The rise in overseas student numbers includes an increase of 15,000, or 54%, in those coming to study from China.

The figures for overseas student numbers in 2011 do show a small fall as the government's new curbs have begun to bite. Issued student visas fell from 271,000 in the year ending June 2011, to 255,000 in the year ending September 2011.

Matt Cavanagh, of the Institute of Public Policy Research, said: "The figures remind us that it was a mistake for the Conservatives to choose 'net immigration' for their overall political target.

"The figures confirm that net immigration in 2010 was the highest on record. Not because immigration is rising – as the ONS makes clear, it has been stable since 2004 – but because emigration is falling.

"The government cannot control emigration, just like it cannot control immigration from the EU, so it ends up trying to clamp down even harder on those areas of immigration it can control. But these are the areas most valuable to our economy, like overseas students and skilled workers from outside the EU."

Labour's immigration spokesman, Chris Bryant, said the fall in the number of illegal entrants – those stopped at British ports this summer – shed light on the home secretary's view that her limited pilot scheme, involving relaxed passport controls, had been a success: "Far from improving the number of detections of people with criminal records or not wanted in this country for other reasons, these figures suggest fewer of those people were stopped," he said.

Sir Andrew Green, of Migrationwatch UK, which campaigns for "zero net migration", said: "At over a quarter of a million in 2010, net migration was the highest it has ever been. It was more than five times the level of 1997 when Labour came to power. It is absolutely vital to get this down to less than 40,000 if we are to keep our population below 70 million."