Thousands of passengers have been left stranded after air regulators grounded Turkmenistan Airlines for safety reasons.
The UK's Civil Aviation Authority said flights from Birmingham and London's Heathrow to Amritsar, and Heathrow to New Delhi - which fly via Ashgabat, Turkmenistan - had been suspended.
The CAA acted after the European Aviation Safety Agency suspended permission for it to fly in the EU.
It also flies from Frankfurt and Paris.
Set up in 1992 by the former Soviet Union state, its route to Amritsar is popular with the British Punjabi population.
The Foreign and Commonwealth Office (FCO) said the European Aviation Safety Agency had suspended the airline's flights to and from the EU "pending confirmation that it meets international air safety standards".
"This means that Turkmenistan Airlines flights between the UK (London Heathrow and Birmingham) and Turkmenistan (Ashgabat), do not have permission to travel to and from the UK," the FCO said.
Affected passengers are advised to contact Turkmenistan Airlines to seek advice, the FCO said.
The budget airline also offers flights from Birmingham and London Heathrow - via Asghabat - to various other locations such as Bangkok and Beijing.
The CAA said: "Passengers who have travelled may need to make their own arrangements to return home".
It lists Air India, British Airways, Jet Airways, Virgin Atlantic and Turkish Airlines as potentially offering alternative routes.
Those who have booked but are now unable to fly will have to contact the airline for a refund.
"Passengers who booked directly with the company via either a credit, charge or debit card may alternatively be able to make a claim against their card provider," the CAA said.
Those who booked through an airline ticket agent, should speak to the agent in the first instance, the CAA said.
The was no obvious information on the company's website which also appeared to be allowing new bookings still to be made.
Can I get my money back?
Passengers seeking a refund for unused tickets are being advised to contact the airline directly
If you've paid by credit card for your flight, and paid more than £100, you may be able to claim compensation from your credit card firm under Section 75 of the Consumer Credit Act 1974.
If you've paid by debit card, and paid more than £100, you could try to contact your bank and ask about "chargeback". However, to get this form of compensation, your bank would need to claw back your money from the airline directly.
If you booked through a travel agent which is ATOL-protected, you may be able to claim compensation via your travel agent.
If you have travel insurance, and your insurance covers insolvency, you may be able to claim from your insurance firm.