The Leicestershire wildfire was one of dozens to break out after dry weather led the Met Office to issue an amber wildfire alert covering large parts of the country on 1 April.
Northern Ireland has since declared a major incident after 146 wildfires broke out since Thursday, Cumbria Fire and Rescue Service said it attended more than 40 blazes across the county over the weekend, with further fires reported in Scotland.
A spokesperson for the National Forest urged people to be cautious in the open countryside during dry weather.
They added: "We are deeply saddened by the recent fire at Bardon Hill in Leicestershire, which sits on the edge of the National Forest.
"While this particular site is not land owned or managed by the National Forest Company, it is part of the wider forest landscape we are all working to protect and enhance.
"This incident highlights the very real danger that fire poses to our woodlands and wildlife, especially during periods of prolonged dry weather."
