Rail commuters face losing up to a third of scheduled services under a mass timetable shake-up, campaigners claim.

More than four million trains are being rescheduled from Sunday, in an overhaul designed to increase overall frequencies and reliability, but some passengers will find their regular journeys are no longer possible.

Departure times will change for every train run by the UK's busiest franchise - Govia Thameslink Railway (GTR) - which consists of Southern, Thameslink, Great Northern and Gatwick Express.

There will be almost 400 additional GTR trains every day.

However, some passengers in a number of locations are complaining they are about to be hit with fewer or slower services, including in Hertfordshire, Bedfordshire, Kent, East Sussex and Surrey, where many pay several thousands of pounds for annual season tickets to London.