Charities will not be allowed to hold Three Peaks Challenge events during any of the school holidays in England, Scotland or Wales under the Institute of Fundraising's revised guidance on outdoor fundraising.
The institute's new code of practice, published last month, contains a separate set of rules that relate only to the Three Peaks Challenge. The rules say members of the institute must avoid holding the events during school holidays in order to reduce overcrowding. Members of the Fundraising Standards Board are also bound by the institute's code.
The Glen Nevis Visitor Centre's events diary, which is published online, shows that five charities and four firms have already arranged to run events on Ben Nevis during the Scottish school holidays in July.
Louise Richards, director of policy and campaigns at the institute, said charities that broke the new code would be referred to the Fundraising Standards Board, but it was unlikely they would be penalised for events that had been booked before the new code was published.
Steve Williams, events coordinator at the Meningitis Trust, which has arranged a Three Peaks event during the Scottish school holidays, said: "The Ben Nevis ranger said it was fine when we booked the event. It's too late to change our plans now, but in future we will consider the institute's new rules.
"The hard bit will be finding a date that is outside all of the holidays, especially when precise dates vary between counties as well as countries."
Katie Elam, a supporter officer at international volunteering charity Skillshare, said she was concerned the new rules could cause overcrowding in April and May. "I think it is too much to put the Scottish school holidays off limits too," she said. "It would be wise to spread the walkers over more weekends, throughout the holidays."