Train passengers have been warned of disruption and fewer services due to action by a rail union.

A ban on overtime by the ASLEF union has prompted Govia Thameslink Railway (GTR), which operates Southern, Gatwick Express and Thameslink services, to run an amended timetable with fewer services.

The amended timetable will run from today until Saturday, May 20.

A spokesman for GTR said the amended timetable will “provide greater certainty for customers on train times with fewer short notice alterations”.

The rail company warned that services are likely to be busier than usual and urged commuters to allow extra time for journeys.

“If you have flexibility on your travel plans, services are normally much quieter on Mondays and Fridays,” the spokesman said.

Services to and from London Victoria will be reduced, with only two trains per hour to Brighton, one train per hour to Eastbourne and one train per hour towards Bognor.

Trains on the East Coastway and West Coastway will also be limited, with only one or two trains operating per hour on routes across Sussex.

The disruption comes as a strike day later this month looms, with ASLEF, the union of train drivers, expected to walk out on Wednesday, May 31.

The industrial action will cause all Southern, Gatwick Express and Thameslink services to be suspended.