UK immigration policy has been criticized after estimates of the number of foreign students who overstay their visas were revealed to be inaccurate.

Prime Minister Theresa May faces mounting pressure to remove overseas students from immigration figures after new data from the Office for National Statistics released on Thursday showed that 4,600 international students remained in the UK after their visas expired last year, compared with the government's previous estimates of around 100,000.

May has repeatedly rejected calls to exclude foreign students from her Conservative government's mooted policy to limit net migration to the UK to the "tens of thousands".

The UK Parliament's Education Committee recently recommended that international students should be listed under a "separate classification" and not be counted against the overall migration limit.

Senior ministers including Chancellor Philip Hammond and Foreign Secretary Boris Johnson have raised concerns that limiting net migration will deter foreign students from coming to the UK.

The ONS data appeared in a Home Office report published this month. The figures are described as "experimental statistics" achieved through an exit check program that analyses passenger ticket bookings, passport swipes at the border and immigration records.

The report found that of the 181,024 international students whose visas expired last year, 97.4 percent departed the UK on time. A minority left after their visas expired.

Tim Bradshaw, director of the Russell Group, an association of 24 UK universities, said: "This exit check data confirms that in addition to helping create a diverse learning environment and making a big economic impact, an overwhelming majority of international students comply fully with the terms of their visas."

Ning Yang, director of admissions at Sunrise Immigration, said it would be "unwise" for the government to include foreign students in its plans to limit migration.

"Chinese students (for instance), are making a contribution to UK economy," Yang said. "Local accommodation, housing, and restaurants all benefit from them."

There are more students from China in the UK than from any other non-EU nation, and China is the only country showing a significant increase in student numbers.

In 2016, 91,215 Chinese students were in the UK for higher education degrees. The number has increased annually by 1.8 percent since 2013.

Cao Yuan, director of admissions agency O4U, said Chinese students still identify the UK as an attractive and economical place to study. "Education in the UK still has a good reputation in China,"Yuan said.

British Home Secretary Amber Rudd has launched an investigation into the impact of international students on the UK's society and economy.