Loch Lomond national park has been accused of “absolute incompetence” after it admitted wrongly charging campervans for staying overnight in lay-bys.

A blunder by the park authority has forced motorhome drivers to buy permits for spending the night at roadside sites since a new camping ban was introduced five months ago. The park says it has made refunds to those affected.

The debacle has been seized on by outdoor campaigners, who say the park’s attempts to restrict camping are doomed to fail. They are calling on ministers to investigate and for “heads to roll”.

Loch Lomond and The Trossachs National Park Authority launched a controversial new scheme banning camping without permits in March. Its aim was to curb anti-social camping, but activists argued it would penalise the majority of responsible campers.

As part of the scheme campervans were charged to stay overnight at lay-bys. But the park has now accepted that this was a mistake, and said that it has refunded £627 worth of fees.

In a circular to campervan owners, it promised refunds for those who had paid for permits at seven sites across the park, including Loch Earn, Bochastle and Tarbet. This was due to “operational changes”, the park said.

In a statement the park authority explained it would “no longer provide permits for motorhomes to stay in lay-bys”. This was because Police Scotland had agreed to use road legislation to deal with “irresponsible use of motor vehicles in lay-bys”.

Cameron McNeish, the well-known outdoors writer and broadcaster who uses a campervan, accused the park authority of creating confusion. “Many folk have told me they simply now avoid the national park as they feel unwelcome,” he told the Sunday Herald.

“Anyone with any knowledge of road traffic law would have been aware that motorhomers and campervanners have every right to stop and spend the night in a lay-by on a public road, so it beggars belief that the national park authority was not aware of that and simply made up their own laws.”

He added: “It really is time Scottish Government ministers stepped in and sorted the absolute muddle created by this park authority. If they do I would expect heads to roll.”

The Parkswatch Scotland blogger, Nick Kempe, described the campervan bungle as “a serious case of public maladministration”. Senior park officials should be held to account and an apology issued, he argued.

“Having spent three years promoting the camping bylaws to local communities and politicians as the only way to prevent vehicle encampments in lay-bys, the park authority has done a u-turn and admitted the police already had all the powers necessary,” he said.

“Their attempt to limit the places where campervans could stop and then charge them for doing so was in complete disregard of traffic law. It was also quite bizarre because they made no attempt to charge caravans for stopping in exactly the same places.”

The veteran outdoor campaigner, Dave Morris, argued that the park was failing to meet its obligations under Scotland’s ‘right to roam’ legislation. “This u-turn demonstrates absolute incompetence at the highest level in the park,” he said.

“Scottish Government ministers responsible for justice and environment need to investigate why this organisation is so ignorant of its duties and role in public life.”

The park authority pointed out that caravanners staying weeks or months on two old stretches of road by Loch Earn had damaged the park’s unique environment. “Our clear legal advice was they weren't part of the formal road network and that the issue could be addressed with bylaws,” said the authority’s chief executive, Gordon Watson.

"Police Scotland have since advised us they will treat these two lay-bys as roads and we are pleased they will enforce traffic laws to address unlawful encampments which have caused major problems in the past while allowing overnight stays by vehicles in these areas.”

Fees of £627 for these areas have been refunded. “We are greatly encouraged by the overwhelmingly positive response from locals and visitors alike to the major improvements which the permit system has introduced,” he said.

“We remain committed to ongoing monitoring and review of the new system to ensure its long-term effectiveness and benefit to the park.”