Netowork Rail was told yesterday that despite nearly £9bn of improvements to the west coast main line, a lack of capacity could mean the service would be unable to meet rising passenger demands within just eight years.

The warning, from Westminster's Public Accounts Committee (PAC), came as Jon Cruddas, one of the contenders for the Labour deputy leadership, called for the railways to be brought back under public control.

In its report out today, the PAC said overcrowding was prevalent on some services and signalled there was "a risk train operators might raise fares on the west coast main line to choke off' demand".

Edward Leigh, PAC chairman, said: "Demand for the services on the west coast main line has grown more quickly than expected and some parts of the route are already at or near capacity. It is extraordinary that in only eight years' time, the line once again may not be able to meet demand."

He called on all the rail bodies as well as the Department for Transport to work together to ensure "greater use of the existing tracks, increase train capacity and minimise disruption to services from work on the track and signalling".

He insisted there must be no suggestion, following such large expenditure, that "railway passengers should simply have to resign themselves to the stress and inconvenience of chronic overcrowding".

Richard Bacon, Conservative MP for South Norfolk and a PAC member, said: "Simply telling commuters who pay £5000 a year for season tickets to accept they may not get a seat is not good enough."

It has been estimated that by introducing longer and more frequent trains the number of seats per hour will, by 2015, hopefully rise by 48% on peak services and by 113% on off-peak ones. Around £100m has already been spent on extending platforms and building new ones.

However, the report pointed out there was only limited scope in the short term for improvements, with one suggestion being to encourage more people to travel at off-peak times.

Passengers were warned they faced further disruption at weekends as maintenance work was carried out for "at least the next five years".

Today in the New Statesman magazine, London MP Mr Cruddas, said: "It's time we began to think the previously unthinkable and bring the rail operating companies back under public control.

"By the government's own reckoning, public subsidy of the railways has now reached an almighty £4.5bn a year, of which £1.4bn is paid to the train operators. Yet, since 1997, the cost of rail travel to consumers has increased by almost 53%."