New timetable arrangements coming into force on the railways this weekend are a "disgusting insult" to disabled passengers, a union has said.

The Rail, Maritime and Transport (RMT) union said the latest instruction from Govia Thameslink Railway (GTR) tells staff not to attempt to place people of reduced mobility on a train if there is a possibility of delaying the service.

RMT general secretary Mick Cash said: "I cannot believe, in this day and age, we are telling staff to ignore the needs of disabled people if the time it will take to deploy a ramp and assist them on to the train will cause a delay.

"They are introducing a policy which effectively means disabled people will not be assisted on to the train and allowed to travel.

"This is outrageous and flies in the face of their Disabled People's Protection Policy which requires them to ensure assistance is available.

"If this is not bad enough, in respect of anyone having a seizure whilst on a train, the guidance says: 'Explain that your first priority is care for the individual, but not taking action will cause thousands of other passengers to be stuck ... Move the ill passenger from the train as quickly as possible'. This is truly shocking advice and an insult to all passengers.

"They now need to be stripped of the franchise to make way for an integrated, publicly-owned operation that is properly equipped to deliver these services."

A spokesman for GTR, which runs services including those on Southern Rail, said: "We place a priority on making our services accessible to all and actively encourage people with restricted mobility to use our trains.

"If any passenger - with accessibility needs or not - arrives late at a station with insufficient time to board, then we can't hold the train at the platform.

"Part of our responsibility is to make sure each service leaves on time to avoid knock-on delays, skipped station stops and cancellations to dozens of other services which would affect thousands of other passengers, many of whom may also be disabled.

"In central London between London Bridge and St Pancras, we've done away with the need for a ramp, by installing humps on every platform to give level access, manned by a member of staff throughout the day."

The company is introducing a new timetable from Sunday, rescheduling every train as it brings in more than 400 extra services a day.