The £2 cap on bus fares in the north of Scotland could halt investment in rail services as passengers desert the more expensive train network, campaigners have said.

Ian Budd, convener of The Friends of the Far North Line, said the Scottish government had "effectively shot themselves in the foot" by capping bus fares, making them far less expensive than rail services covering the same route.

While a single bus journey from Thurso to Inverness now costs just £2, the same journey by train costs between £16.60 and £28.

Transport Scotland told the BBC it would continue to monitor the impact of the £2 bus fare cap on passenger numbers and wider transport behaviour.

On Wednesday, Scotrail's managing director Joanne Maguire told the Scottish Parliament's transport committee that the state-owned rail provider will lose £750,000 annually in the Highlands as a result of the bus fare cap, which started earlier this year - a revenue drop of 12%.

Budd, who campaigns for improvements to the Far North Line, questioned the logic behind the £2 cap in an area where the bus and train followed the same route, calling it an "extraordinary ill-considered plan".

"The fact that you're now putting funding into private bus companies competing with a state-owned railway just shows a lack of understanding of the whole transport network," he said.

Budd said the line north of Inverness needed upgrading but he feared the business case for making improvements was being damaged by the falling revenues.

He said the line was a single track line - meaning trains must wait in limited passing loops if another train is coming the other way.

This makes the timetable "very vulnerable", he said.

But he believes it could become reliable "if enough money is spent on infrastructure improvements which are needed".

Ember are the only bus provider running services from Thurso and Wick to Inverness after Stagecoach ceased operating this route in October.

They run up to eight return buses a day at a maximum cost of £2 per trip.

The Scottish government said a single ticket on the previously operating Stagecoach service from Wick to Inverness cost £31.

Trains on the same route cost between £16.60 and £28 for a single and can take up to an hour longer than Ember's bus services.

Other stops on the line include Dingwall, just 14 miles away from Inverness, which costs £8.80 for a train journey.

Brora, 56 miles away, costs £26.30 for a single rail trip.

A Transport Scotland spokesperson said "The Scottish government wants more people to travel by public transport.

"The £2 Bus Fare Cap is one of a number of measures supporting households with the cost of living.

"These also include the permanent removal of ScotRail peak rail fares and continuing to provide free bus travel for under 22s, over 60s and disabled people."