Rail fares could rocket because of loopholes in new contracts with privatised train companies, passengers were warned today.

Some ticket prices could almost double within five years, claims environmental pressure group Transport 2000.

Ticket rises on key commuter routes are carefully regulated and are also linked to the performance of individual train companies.

But under new regulations all standard, first-class single and open return fares would remain unregulated, leaving train companies with the option to increase them at will.

Transport 2000 executive director Stephen Joseph said: "We are extremely concerned that too many rail fares remain unregulated in the contracts soon to be signed with rail companies. We want to see the next government instruct the Strategic Rail Authority to draw up tougher rules on fares as part of a wholesale review of rail fares policy."

He added that although there were many book-ahead bargains, turn-up-and-walk-on fares had soared.

Transport 2000, which advised Labour on road and rail issues before the last election, based the predictions on the biggest rises brought in between June 1995 and January 2000 - including those on Sir Richard Branson's Virgin services.

Alan Hyde, spokesman for York-based train operator GNER, said: "These figures should set alarm bells ringing for passengers. These figures are heavily-based on Virgin's fare increases, and if they are granted the East Coast Main Line franchise, maybe the fares will soar as Transport 2000 predicts. We are committed to providing value for money, our fares have actually decreased in real terms by nearly two per cent since we took over running the franchise."

A spokesman for Virgin said: "We have not planned our fares for the next five years yet. What a company has done in the past does not necessarily have any bearing for the future."

Updated: 10:20 Wednesday, May 30, 2001