There are a few options, but it really depends on where you're stalking in the country, and the topography that surrounds you.
As you're talking about none commercial activity, you could explore Amateur Radio, which has a UK Network of Repeater Stations on voice in UHF, VHF, and HF bands. There's also the message sending APRS network, which may or may not be useful.
In terms of an Amateur Licence, the actual Licence is free, and renewable online every five years, the initial Foundation Course can be completed on a couple of evenings or a weekend if preferred, and that includes the examination, so you'd be able to apply for the free licence and be given your unique M6xxx callsign within a few days.
Being a licensed Radio Amateur or HAM as they say in the US, on a foundation licence, allows you to use up to 10 Watts of power on all frequencies available to Amateurs, and include the following useful bands on HF 1.81-2.0MHz (160m), 3.5-3.8MHz (80m), and 7.0-7.2MHz (40m), plus access to the 28.0-29.7MHz (10m) band to access fixed UK HF Repeaters. At VHF you'd have 50.0-52.0MHz (6m), 70.0-70.5MHz (4m), and 144-146MHz (2m), at UHF you'd have the 430-440MHz (70cm) band.
There are fixed UK Repeater Networks on 6m, 2m, and 70cm.
Take a Look here
ukrepeaters HOME PAGE
The reason I mentioned 160m, 80m, and 40m, is because these are all bands used for Near Vertical Incident Skywave (NVIS), which allows communications up to 200 miles in deep forest, or between mountain valleys, anywhere with no line of sight communications. However, antennas can consist of long wires for fixed stations, and loops or angled whips on vehicles. Antennas on foot might be a challenge, but certainly angled whips or small tuned loops could be fitted to an Argocat six wheel vehicle with some thought.
You can read some useful information on NVIS propagation here
Propagation | WWW.RAYNET-HF.NET
Basically, you use the option that works for you in the circumstances.
They don't call me wireless for nothing...