Tory MPs are calling for the Government to reverse plans to increase fares on Southern Railway.

Regulated fares will go up 1.9% across Britain's railways next year as the annual rise is linked to July's Retail Price Index (RPI) measure of inflation, which was announced by the Office for National Statistics on Tuesday.

But Conservative ministers are coming under pressure from MPs in their own party not to implement the rise for Southern passengers, who have faced months of delays and cancellations.

Tim Loughton, MP for East Worthing and Shoreham, said he has written to Transport Secretary Chris Grayling to call for fares to be frozen across the network operated by Southern's parent company Govia Thameslink Railway "until they start to run a proper service".

He described any increase in ticket prices as "completely untenable in current chaos".

Nick Herbert, MP for Arundel and South Downs, commented: "Any fare increase at all in the current circumstances, even at just the rate of inflation, will add insult to injury.

"If anything passengers feel they should be getting money back as proper compensation for the daily travel misery they've had to endure."

Rail Minister Paul Maynard said passengers "want more reliable journeys in comfort and with better facilities".

Southern passengers have suffered major disruption because of a dispute over changes to the role of conductors and staff shortages - blamed by the company on high levels of employee sickness.

Around half of rail fares are regulated, including season tickets on most commuter journeys, some off-peak return tickets on long distance trips and Anytime tickets around major cities.

A 1.9% rise would add more than £78 to the cost of a Brighton to London Victoria season ticket.

Unregulated fares, such as off-peak leisure tickets, will be increased by whatever amount the train companies decide.

Transport Focus, Railfuture and the Campaign for Better Transport all called on ministers to use the Consumer Price Index (CPI) measure of inflation for setting fares, rather than RPI.

CPI, which was 0.6% in July, is used for calculating pensions and most benefits.

Research by the TUC and the Action For Rail union campaign showed that fares have risen by double the speed of wages since 2010.

The analysis revealed that fares have increased by 25% in the last six years, while average weekly earnings have grown by 12%.

A series of protests were held at railway stations across the country by trade unions on Tuesday morning.

Labour leader Jeremy Corbyn held a placard which read "2017 rip off central" at a demonstration outside London Bridge station.

TUC general secretary Frances O'Grady said: "It's time for rail services to be publicly owned, saving money for passengers and taxpayers alike.

"Instead of increasing fares and cutting staff, we should be building an accessible, reliable train service that Britain can be proud of."

Mr Maynard insisted that "ages are growing faster than train ticket prices".

He added: "Passengers want more reliable journeys in comfort and with better facilities. That is why we are investing record amounts in our railways delivering the biggest rail modernisation programme for over a century, providing more seats, more services, wi-fi and air conditioning."

Paul Plummer, chief executive at the Rail Delivery Group, representing train operators and Network Rail, said: "Increases to season tickets are set by Government. For every pound paid in fares, 97p goes back into running and improving services and it's our job to make sure that money is spent well."