More than 130,000 acres of Cumbria and Lancashire could be added to the Lake District and Yorkshire Dales national parks if proposals by Natural England are approved.
The agency has recently resumed work to identify extensions to the national parks after halting its studies last year during the public inquiry into the South Downs listing.
The planning inspector favoured Natural England's approach to designating national parks and confirmed they can be based around more than one form of landscape character.
Areas such as Howgill Fells and Mallerstang, both near Sedburgh in south Cumbria, are among those being considered for national park protection.
Helen Phillips, chief executive of Natural England, said: "Looking at whether areas can be included as part of the Lake District and Yorkshire Dales national parks remains a high priority.
"The legal uncertainties of recent years have caused significant delays and we are looking into how we can progress the project quickly but thoroughly. We are committed to holding a full public consultation to provide all stakeholders the opportunity to tell us their views."