Transport chiefs are calling on ministers to give commuters a "right to flush" on trains.

At present railway firms are not obliged to provide toilets for customer use during journeys.

Craig Turton, deputy chairman of the environment committee at Brighton and Hove City Council, has written to the Department for Transport to demand the law be changed.

Last year there were complaints that loos on Southern Railway trains between Brighton and London were frequently out of order.

In a letter to Tom Harris MP, parliamentary under-secretary of state for transport, Coun Turton said, as a commuter to London, he had often seen passengers getting off trains to use toilets at stations before reaching their destination.

He said: "This issue potentially affects every single rail passenger across the UK.

"Until passengers have a legal right to flush, those who may have to use a toilet at short notice, such as people with a disability or medical condition, older people, parents with young children and pregnant women, will not have the security of knowing that legally the train they board has to have fully functional toilet facilities.

"Would you not agree that it is contrary to the spirit of the Disability Discrimination Act and human rights legislation, to which this Government has demonstrated its commitment, for the Department for Transport to have no plans to ensure train operators are legally required to provide working toilets on trains?"

Last October Brighton and Hove City Council passed a motion calling for a change in the law and stated there were problems with toilets on Southern trains. Derek Twigg MP, predecessor to Mr Harris, responded by saying there were no plans to make toilet maintenance a legal requirement.

With his letter to Mr Harris, Coun Turton sent copies of responses from passengers.

Chris Hudson, spokesman for Southern Railway, said the firm followed up the concerns raised by the council's motion last year.

He said: "It is understandable for passengers to expect clean, useable toilet facilities on our class 377 fleet of trains. We have had a spate of problems with these in the past but we have now completed a programme of modifications which have largely improved reliability. We are now typically seeing in excess of 90 per cent of our toilets available across all our trains at any one time.

"Each four-car set has two toilets. The likelihood of both being out of action now is extremely small so one would expect a working toilet to be on every train."

A train environment desk has been set up in the control room to respond to problems with toilets, graffiti and vandalism and there is a team of mobile engineers to fix trains.