The reopening of a railway line between the Scottish Borders and Edinburgh is an example of Britain's lack of ambition compared with its European neighbours, an expert has said.

The link between the capital city and Tweedbank will re-establish part of the former Waverley line, which fell victim to the notorious Beeching cuts in the 1960s.

But concerns have been raised about the Borders Railway because it is mostly single track rather than double - potentially increasing the likelihood of disruption to services - and not electrified, which means slower, "dirty" diesel trains will be used.

Mark Smith, who runs rail website The Man In Seat 61, said the project showed how Britain does things differently from its continental neighbours.

"The French build a cathedral. I remember looking at a station in Lyon which, I think, had three trains a day at the time and thinking 'Wow, they've got some confidence'.

"We, of course, do it the other way round," he told the Press Association.

"We dip our toe in the water. So the figures back up the single-track diesel line - I'm sure it's going to be a rip-roaring success - then we start thinking about 'Maybe we should have made it double-track, maybe we should be electrifying it'."

He said rail investors in Britain "take a very hard line with the finances", which means "we look seven years into the future, not 30".

Mr Smith added: "Very often we do things like this but there's no reason why it cannot be a success and then you can start putting in double track and electrification later if you need to."

But the Campaign For Borders Rail has raised concerns about how the network - which opens this weekend - will cope with growing demand.

Simon Walton, chairman of the group, said: "The whole concept of future-proofing is something that we feel hasn't been addressed adequately.

"Our main concern is the reduction in the length of double track on the line. The original plan was 16 miles and it's been reduced to nine-and-a-half.

"Operationally it makes it very difficult to maintain the scheduled service. I hope I will be proved wrong but there isn't a great margin for error."

Campaigners vigorously argued "right up to ministerial level" about the decision to install several new bridges that are too small for a second track to be added later.

"We thought that was a constraint built into the project that could have been avoided for little extra expenditure," Mr Walton said.

Mr Smith, who used to set fares at the Department for Transport, also noted that the Borders Railway - which cost £294 million at 2012 prices - has missed out on the benefits of going further south.

"It would be lovely if it linked up to Carlisle and formed a complete route to Scotland, but it might do yet in the future," he said.

The Borders Railway website describes the 30-mile (48km) project as "the longest new domestic railway to be constructed in Britain for over 100 years", although it mostly follows an old route which was shut in the 1960s.

Mark Dewell, who has worked on several heritage train projects including the Epping Ongar Railway in Essex, said the new scheme was not "enormous" in the context of track reopened by volunteers in Britain over the years.

He noted that there are now more than 500 miles (805km) of heritage railway lines around the country.

"If it was all put end to end it would go from London to Glasgow, all built and run by volunteers," he said.

"Thirty miles of new railway - it is very nice to hear about but it's not an enormous amount in that context."