After a “technical issue” was found on the 15-minute service trains, the majority of them have been withdrawn from service for safety checks.

As a result, Heathrow Connect trains are being switched over to the faster service, allowing it to continue to operate four times an hour.

Anyone wishing to go to stops on the connect routes should take the 140 bus from Heathrow to Hayes & Harlington where they can then access additional Great Western Railway services to Paddington.

Meanwhile, Heathrow Express tickets will be reduced during this period with a single ticket costing £17 and a return costing £28.

Pre-bought Heathrow Connect tickets will be accepted on the Heathrow Express service. Any customers who have purchased Business First tickets from Heathrow Express will be entitled to a full refund. 

Heathrow Express director Fraser Brown said: “While we regret the inconvenience this will cause to our customers and airport colleagues, safety remains our top priority.

“We are working with Siemens engineers, who manage our depot site and the maintenance of our trains, to understand the extent of this issue.

“When we are aware of what we are dealing with, we will be able to make a decision on when a full service will resume.”