The number of rail passengers will soar by at least 30 per cent within the next decade, train firms have predicted.

Southern Trains and First Capital Connect, which run services from Sussex to London and beyond, have warned the number of people travelling, particularly at rush hour, is likely to have risen by about a third by 2016.

The additional passengers will put extra pressure on already overcrowded carriages on the busy Brighton line.

The rail companies said they would do all they can to accommodate the extra customers.

But they added that a change in commuters' travelling behaviour and working hours was also needed to ensure the railways can cope with the strain.

The predicted increase in numbers is attributed to Sussex's growing population, made worse by the county's intensive homebuilding plans.

People living in the area are also increasingly likely to work in London.

Chris Hudson, media relations manager for Southern Trains, said service use was expected to grow by three per cent a year.

He said: "The transport infrastructure has got to be able to cope with that.

Under pressure "The problems are the peak times when trains are at their limits, on the Brighton line particularly.

"We'd like to see the most growth off-peak."

Southern Trains' franchise to operate between Sussex and London ends in 2009.

If it wins a renewed contract, Mr Hudson said the firm should be able to cope with the extra passengers it expects in the next six or seven years within its existing infrastructure.

By 2013 or 2014, the Thameslink project, formerly known as Thameslink 2000, should have been completed.

The scheme will take pressure off the Brighton to London line by expanding rush hour capacity and vastly increasing the number of services from the South Coast to London.

But Mr Hudson stressed customers should still try to travel at off-peak times and the company would continue to encourage this by offering reduced fares.

Sarah Critchley, spokeswoman for First Capital Connect, said the company expected to add three or four per cent each year to passenger numbers.

She said: "We have a number of options available to us to manage the extra capacity.

"These include redeployment of rolling stock, redesigning timetables, and working with the Department for Transport on other options."

The firm began a seven-year franchise in April this year, running trains between Brighton, London and Bedford.

It took over from Thameslink, which was run by the Go Ahead Group, and Great Northern, which was operated by National Express.