Two would-be Kent Labour MPs have called for the country's railways to be renationalised, saying the move could provide money to keep fares down.

Tris Osborne, the prospective parliamentary candidate for Chatham and Aylesford and Clair Hawkins, the prospective candidate for Dover and Deal, have signed a letter saying they want to see a not-for-profit model for the rail network.

Spiralling ticket prices are likely to be among key issues for voters in the general election and it is a topic on which the Conservatives in marginal seats in commuter towns are known to feel vulnerable.

The cost of travel for rail commuters in Kent is one of the highest in the UK. Rail fares for Kent commuters went up less than had been expected this year after the government said train operators would not be allowed to increase them by 1% above inflation. It meant that average regulated fares went up by 3.1% rather than the planned 4.1%.

In the letter to The Observer, the candidates are among 30 to say a policy of gradual renationalisation would allow fares to be kept under control and profits to be reinvested in services.

They argue that under the present franchising system, private companies can charge high fares and "walk away with hundreds of millions of pounds every year, despite running monopoly services and benefiting from £4bn of public investment in the rail network every year".

"Labour's response to this should be to offer a fairer deal to commuters as a part of Ed Miliband's response to the cost of living crisis. Just as Labour has pledged to freeze energy bills and reset the market to secure a better deal for customers, so it will be necessary to reform the rail industry to secure a better deal for passengers."

The letter points to the example of the East Coast line, saying it shows there is a better way to run Britain's rail services.