Plans to ramp up rail services have been brought forward by a week and will start from next Monday, a union is claiming.

Services were expected to be increased gradually from May 18 as part of an easing of the economic lockdown.

The Rail, Maritime and Transport union (RMT) said it had discovered that the plans had been brought forward to start on Monday May 11.

Officials said the industry had been told to be ready to begin a last-minute mobilisation to accommodate an increase in passenger numbers from Monday in reaction to the Prime Minister's address on Sunday.

The RMT said the move overrules a planning document sent to the unions on Thursday by the Rail Industry Coronavirus Forum, a rail industry and trade union body established to put in place arrangements to protect passengers and workers.

The document said services would be increased in phases, with a "stepped" increase from May 18, said the RMT.

General secretary Mick Cash said: "We have it on good authority that the rail network has been put on notice to begin a last-minute mobilisation to accommodate an increase in passenger numbers from Monday.

"This is earlier than expected and completely contradicts assurances sent to us only yesterday that the rail industry had only put in place services and arrangements to protect passengers and workers from a 'not high' increase in passenger numbers at a later date.

"To overrule the rail industry like this is a complete breach in faith of the trade union and rail industry discussions.

"It is also a high-risk strategy and RMT is deeply concerned that rushed political considerations could well override the safety issues for staff and passengers alike.

"RMT will not compromise on the health, safety and livelihoods of our members and we will not agree to anything that fails to put the safety of staff and passengers first. If that means advising our members not to work under conditions that are unsafe and in breach of the Government's and industry's own guidelines then that is exactly what we will do."

A Department for Transport spokesman said: "We are examining a range of options on how transport can respond to support the recovery in a timely way when the time comes and it is safe to do so. We continue to prepare for any scenario."

A spokesman for the Rail Delivery Group, which represents train operators and Network Rail, said: "When Government decides the time is right, the railway will respond to support the nation during the next phase of the coronavirus response, as it has done throughout the lockdown.

"Our priority will continue to be the safety of our staff and passengers and we will work closely with Government and unions to run trains safely while supporting the economy and the public's health."

Mick Whelan, general secretary of the train drivers union Aslef, said: "We have worked with the Government and all stakeholders in the rail industry throughout this crisis to ensure that key workers get to work, and food and medical supplies are moved around the country.

"We want to help Britain return to what we knew as normal before the pandemic, and have agreed with the Department for Transport that we will increase the number of services when and where it is safe for passengers and for staff."