The rest of the 5 hours can be just navigation away from airfield...
To be a Navigation flight acceptable for licence issue it must include turning points. i.e you must have flown a navigation route.
Quote directed from LASORS: '‘Cross-country flight’ means any flight during the course of which the aircraft is more than 3 nautical miles from the aerodrome of departure.'...
This definition of Cross Country originates in the ANO Schedule 8 Part B Section1
2 For the purposes of this Section:
"Cross-country flight" means any flight during the course of which the aircraft is more than 3 nautical miles from the aerodrome of departure.
and
"this section" relates solely to the FI ratings and is used to defining those flights that a FI (Restricted) cannot authorise. i.e. the first solo flight that goes more than 3 miles from the airfield. It is not for the purpose of defining a navigation cross country flight required to qualify for the issue of a PPL!
The only flights that need a signature when visiting another aerodrome are those on the Qualifying Cross Country using this form:
http://www.caa.co.uk/docs/33/SRG2105FF.pdf