More than half a million passengers have used the Borders Railway in its first five months, exceeding predictions.

The 30-mile line, which opened in September, is the longest new domestic railway built in the UK for over a century and runs from Edinburgh through Midlothian to Tweedbank in the Borders.

Initial predictions were for the service to carry 650,000 passengers in its first year, however rail bosses marked the 500,000 journey milestone at Edinburgh Waverley on Thursday.

The new service has been popular with tourists, commuters and the Queen, who spent the day she became Britain's longest-serving monarch travelling on the line.

It runs on part of the former Waverley line, which was closed during the controversial Beeching cuts in 1969, leaving the Borders region without any access to the National Rail network.

Transport minister Derek Mackay said the near £300m investment in the service has been worth it.

He said: "We knew it would be a success and a wise investment but it's even more popular than we thought. I think it's been vindicated and is making a difference. Rail requires huge infrastructure support, and it has that. Rail in Scotland is very popular at the moment. This service works because it is reconnecting communities between Edinburgh, Midlothian and the Borders and is creating economic opportunities as well as a commuter link."

Selkirk couple Sarah Eno and Andy Swales alighted the train at Waverley to be told they were the travellers who took the service over the 500,000 passenger milestone.

Mr Swales, 67, said: "We were one of the first paying passengers on the train and we've used it a couple of times a month since then. Before we either had to drive or take a not very nice bus journey, so this is luxury compared to that."

Ms Eno, 68, added: "There was initially a big boost and I noticed a lot more people coming to the Borders, but it was a beautiful September and October. I think if they put more bike spaces on the trains it would help because the Borders is a terrific cycling area."

The pair said the success supported the case for extending the line further, and potentially into England.

Mr Swales said: "It deserves to go at least as far as Hawick because that's the biggest town in the area, and travel south to England isn't very easy so it would be great if it went all the way through to Carlisle."

ScotRail Alliance managing director Phil Verster said officials were looking at plans to boost the service to cope with demand.

"We've had challenges to maintain enough carriages on this service because it has been popular, but our future plans are to add carriages to our overall fleet and we will strengthen services continuously to meet demand," said Mr Verster.

"Every opportunity to extend the railway to Hawick, and even further to Carlisle, must be evaluated and could hold very exciting possibilities for us."