Theresa May has been told Britain must ditch its border controls in return for a trade deal with India, with the UK warned by officials that it “needs Indians”.

Ahead of the Prime Minister’s two-day visit to India, figures have blasted the government’s crackdown on bogus students and colleges, and new rules to stop companies replacement of British IT professionals with much cheaper Indian workers.

Dinesh Patnaik, India’s High Commissioner in London, said: “Students, tourists and short-term visitors are not migrants under any definition.

“Post-Brexit, you need Indians. Our tourists… don’t come to Britain due to difficult visa conditions.”

Spokesman for the Indian government, Vikas Swarup, told the Observer May faces questions over immigration rules upon her arrival in India, where she will be accompanied by 40 business leaders on the trade mission.

“In the last five years or so, the number of Indian students enrolling in UK universities has gone down by almost 50%; from around 40,000 to about 20,000 now. This has happened because of restrictions on post-study stay in the UK.

“We will continue to raise our concerns regarding mobility with the UK. Mobility of people is closely linked to free flow of finance, goods and services.”

Soon after coming to power the government identified the abuse of student visas as a major source of illegal immigration. A 2012 report into the points-based system for student visas, which was introduced by the previous Labour government in 2008, estimated that 40,000 to 50,000 of the “students” admitted in its first year were bogus and entered Britain to work illegally.

The government’s 2011 pilot scheme which interviewed potential foreign students to test their credibility found a massive 59 per cent of Indian applicants were likely to be bogus students looking to become illegal immigrants, independent migration research group MigrationWatch UK reported.

In August this year a delegation of UK MPs warned in Jalandhar that illegal migration from India is undermining relations between the two countries. Tory Bob Blackman highlighted the role of student visas in this process.

“A majority of the Asia Pacific students are still coming to the UK to work as a cheap labour and not for studying. In 2013, we cracked a whip on around 200 fake universities which were running from single rooms and had intruded deep into our migration system”, the Harrow East MP told a conference on “Migration and Other Diaspora Issues”.

Recent changes to the UK’s visa policy for non-EU nationals also attracted criticism from India ahead of May’s visit. New rules released Thursday will see a raise in the salary threshold for intra-company (ICT) worker transfers from outside the EU.

Indian tech company Nasscom said: “A system that restricts the UK’s ability to access talent is also likely to restrict the growth and productivity of the UK economy.”

The move to tighten ICTs follows years of warnings that the system, intended for employees of multinational companies who are being transferred by their overseas employer to a UK branch of the body, is being used to replace British workers with cheaper Indian labour, and relocate British jobs to India.

Nearly 90 per cent of all ICTs are to Indian workers in the field of IT, while the unemployment rate of UK graduates in computer science is higher than in any other field.

Expressing disappointment with the change in visa policy, Nasscom called for governments and multinational corporations like itself to work together to fight “anti-globalist and protectionist forces”.

“These global challenges cannot be met by the industry acting alone. It needs government support,” company president R Chandrashekhar said.