THE "novelty factor" of the new Borders Railway is contributing to overcrowding on trains, the operator has said amid criticism that some passengers have been left to stand for the hour-long journey.

Campaigners said ScotRail had reneged on a pledge to run longer trains immediately after the launch of the new service to help cope with demand.

However, passengers have taken to Twitter in recent days to complain that the trains between Edinburgh and Tweedbank were often only two-carriages long, forcing passengers including children to stand in the aisles.

In some cases passengers were left at platforms because the trains were already too busy.

The Campaign for Borders Rail said their monitoring also indicated that in the first week of operation, a "significant proportion" of trains had run more than 10 minutes late and some arrived up to 17 minutes behind schedule.

CBR chairman Simon Walton said: “We did expect ScotRail to honour pledges to lengthen all trains in the early weeks to cope with demand - but that hasn’t been the case, with many running in the very minimum two-car formations and consequent overcrowding on some services.”

The Borders Railway opened to the public on Sunday September 6, and was officially opened by the Queen three days later.

ScotRail said last week's disruption had been caused by factors including a train breaking down, signal problems, high passenger numbers and disruptive travellers.

The operator has not disclosed its passenger figures for the route's first week of operation, but said it had been particularly busy with families taking day trips at the weekend. It would take time to establish what "normal" passenger traffic is once the "novelty factor" wore off, said ScotRail.

A spokeswoman for ScotRail added: "We are continuing to monitor passenger numbers so we can tailor how to make best use of the carriages available to us. For example, we may have found a way to temporarily double the number of carriages on a Sunday, and aim to do the same on Saturdays during peak times. We are also planning to add carriages in the short term to one particularly busy service, the 16:24 from Edinburgh - Tweedbank which is key for commuters.

"The Borders Railway is undoubtedly going to be very popular with commuters and leisure travellers alike and we remain committed to achieving the best balance so that customers have an enjoyable experience."