Trains into London on Brighton mainline will still be overcrowded in 2031, a report by Network Rail has revealed.

Despite measures to increase capacity by adding extra carriages to trains and the introduction of the Thameslink to ease pressure on the line, officials admit hundreds of passengers will still have to stand between Brighton and London in 20 years.

During peak hours it is predicted there will still be 1,600 more passengers than seats on the Brighton main line in 2031 with trains to London Bridge most affected.

Passenger rights campaigners are concerned the route will be perceived as a lower priority for investment than other lines that have even greater overcrowding and that fares will be repeatedly pushed up to try to control demand by deterring travellers from using the network.

Network Rail's London and South East Route Utilisation Strategy, which was drawn up with officials from the Department for Transport, looks into the possibility of building a second Brighton main line to reduce overcrowding but this was dismissed on grounds of cost and effectiveness.

A proposed new tunnel from outer London to create additional train paths on the route was also rejected for offering poor value for money but will be kept under review if demand increases as it is seen as the only way of increasing the number of services that can be run.

The report indicated that it would be difficult for train operators to add any more services per hour from London Bridge because of constraints at East Croydon.

Sharon Hedges, from campaign group Passenger Focus, said: “The report clearly indicates some real challenges for rail companies and passengers who face the prospect of more trains being overcrowded for longer.

“What we want to ensure is that train companies don't use fare increases to manage demand which will have serious connotations for people on low wages who cannot change their travel plans.

“There are definitely no easy solutions for the Sussex area but there are other places with higher overcrowding which will get first bite of any investment.”

A Network Rail spokesman said: “We think we have come up with a good plan in place to keep up with expected demand in Sussex.

“There is only so far you can upgrade a piece of railway before it reaches complete capacity so we have to look at other ways.

“This can be done by building new lines or by using flexible ticketing and working with businesses to develop flexible working to spread out the rush hour.”

A three month consultation exercise will now be held into the report's findings.