The government’s announcement that almost all foreigners will require online permission to change planes in the UK from next year has caused consternation at Heathrow – with fears of huge financial losses as a possible four million passengers choose other hub airports to avoid the added red tape.

From April 2025, overseas transit passengers at Heathrow must register and pay £10 for an Electronic Travel Authorisation (ETA) just to spend two hours between flights. Other leading hubs have no such obligation. Losing connecting travellers could undermine the viability of some air routes, further damaging inbound tourism.

Labour has decided to back the Tories’ scheme to require all non-British or Irish nationals to have online permits ahead of travel to the UK.

On Tuesday the minister for Migration and Citizenship, Seema Malhotra, announced the ETA scheme will apply to the vast majority of overseas arrivals by 2 April 2025.

In backing the previous government’s plans, she said: “Digitisation enables a smooth experience for the millions of people who pass through the border every year, including the visitors we warmly welcome to the UK who are predicted to contribute over £32bn to our tourism economy this year.”

Read more: What is the UK’s new ETA travel scheme with a £10 charge – and what does it mean for visitors?

But analysis by The Independent indicates the scheme as planned will cause serious financial damage for Heathrow airport and its retailers, as well as UK airlines.

The demand for transit passengers to apply online and pay for a permit will make London Heathrow an outlier. Other global hubs – including Amsterdam, Frankfurt, Istanbul, Paris CDG, Dubai and Singapore – require only that travellers have permission to enter their final destination.

The government says: “Requiring transit passengers to obtain an ETA stops people who may use connecting flights to avoid gaining permission to travel to the UK.”

At present ETAs are required by six Gulf nations: Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the UAE.

In July, Heathrow airport revealed that 90,000 potential passengers had switched to other airport in the few months since the scheme began for nationals of the first half-dozen countries.

“We’ve seen the loss of a significant number of transfer passengers already,” a Heathrow spokesperson said.

The Independent has extrapolated these figures to model the potential impact were passengers from other nations to follow the same pattern.

At present almost all transit passengers at Heathrow – comprising 30 per cent of the total – need only to be documented for their destination.

But initial figures for Gulf nationals suggest one in six prospective transit passengers has switched from Heathrow to a different hub because of the ETA demand.

From April 2025, though, almost all “airside” transit travellers will need ETAs. If the same proportion is deterred, Heathrow’s passenger figures could fall by four million.

British Airways would sustain the most damage from a slump in transit passengers, with Virgin Atlantic also hard hit. Heathrow is also a key hub for the Star Alliance, offering connections between carriers such as Lufthansa, United, Air Canada and Singapore Airlines.

A significant number of flights at Heathrow rely on transit passengers to be profitable, and some links could be jeopardised if the number of connecting travellers dwindles. In addition many airport retailers are dependent on connecting travellers spending cash as they wait for onward flights.

Calculating the loss to the UK economy of the policy is fraught with complication, but The Independent estimates it is likely to be in the range from £2.5bn to £5bn annually, counting lost revenue to airlines and spending in airport shops.

Airlines that allow an incorrectly documented passenger to fly to the UK without an ETA will face a fine of up to £2,000.

Heathrow and the Home Office have so far declined to comment on The Independent’s calculations. But an airport spokesperson said: “We don’t disagree with the long-term roll-out of the scheme, but including airside transit passengers will make the UK less competitive and harm economic growth.

“We want to work in partnership with Home Office ministers over the next few months to address this issue.”

While Heathrow is not the only UK airport with airside transit, very few passengers elsewhere are on connecting international flights. The impact of the ETA demand is expected to be minimal at other airports.