In a statement the National Trust confirmed that a handful of agencies have been approached, with a pitch process set to take place in December.
PRWeek understands that Unity, The Academy, Slam, Mischief and Hope & Glory have been asked to pitch.
The National Trust has been working with Mischief since 2011.
The review is being overseen by senior PR officer Laura Appleby and follows a procurement audit. The brief is open to enable creativity and different PR channels including traditional and social, with a flexible budget to accommodate this.
A statement from National Trust said: "The successful agency will work with the trust’s national and regional teams to deliver integrated, exciting and impactful PR activity throughout 2015, with the aim of raising awareness of the charity’s mission to champion the importance of special places and deepen the connection people have with the natural world."