Kent's £6bn high-speed rail line has attracted far fewer international customers than forecast, it's been revealed.

The National Audit Office said the actual number of international passengers on the line, which links the Channel Tunnel in Folkestone to London, was just two-thirds what was predicted, a report out today has said.

Although it had "brought a number of significant benefits - including quicker journeys for passengers" - the optomistic passenger predictions had exposed the taxpayer to risk.

It also cost 18% more than the target, although this was delivered within the overall funding and timescale available for the project, the report said.

It added: "Despite missing these targets, this performance compares well with other railway projects.

"The line has performed well since it opened, with only 0.43 per cent of services being delayed in 2010-11 by infrastructure incidents, such as track or signal failures."

It said the High Speed 1 project has delivered a high performing line, which was subsequently sold in a well-managed way which removed the taxpayer's support for the project.

London & Continental Railways Ltd (LCR), which is owned by the Department for Transport, is in partnership with private sector developers at King's Cross and Stratford.

The original business case in 1998 was based on benefits to transport users from faster journey times and increased rail capacity and regeneration benefits.

According to today's report, the total value of these benefits is not known as the Department for Transport has started to identify the methods it will use to evaluate the project's costs and benefits.

The Department has not reassessed these costs and benefits since 2001, despite assurances to the Public Accounts Committee that it would do so.

Railway expert Sim Harris said today that budget airlines were behind the lower numbers.

However, Eurostar has grabbed a huge share of the London-Paris-Brussels market, forcing many airlines to reduce flights.