In Europe most overlanders and offroaders still use CB radio (11m band) or as Dave also already wrote PMR446 (with all its disadvantages). However, HAM radio is also on the rise in this area. Because it simply offers many advantages, possibilities and is also a great hobby.
The regulations might be different from country to country. In the UK you have three license classes, with the right to different technical possibilities and also different learning requirements. In Germany, for example, we have only two so far - a pure beginner and user class is to come. In mobile comms often the 2m or 70 cm band is used. Commonly used voice calling frequencies in Europe are 433.500 MHz on 70cm and 145.500 MHz on 2m.
If you want to dive deeper into the subject, it is always worthwhile to look at the page of the local authority/ regulator. For the UK, this is the
OFCOM. On their website you can find a lot of information about amateur radio in the UK:
Guidance for amateur radio users, sometimes known as ham radio, which is both a hobby and a service that uses various types of radio equipment.
www.ofcom.org.uk
I would say it's worth looking into. But of course it's also important that you choose the radio application that most of the people you're traveling with have.