According to the sources in the government, all British citizens arriving in India from Monday will face a mandatory 10-day quarantine irrespective of vaccination status, in a reciprocal measure over the UK's hugely controversial similar rules for residents of several countries including India.

"From October 4, all UK nationals arriving in India from the UK, irrespective of their vaccination status, will have to undertake three COVID-19 RT-PCR tests - within 72 hours before travel, on arrival at the airport, and on Day 8 after arrival, and mandatory quarantine at home or in the destination address for 10 days after arrival in India," sources said.

Under travel rules unveiled last month, fully dosed arrivals from several nations are being allowed to enter England without quarantine starting October 4. But vaccinated people from vast swathes of the world still face tougher restrictions, including a 10-day home isolation period.

India's Foreign Secretary Harsh Shringla called the rules "discriminatory" and warned that "reciprocal action" may be warranted.