In reply to Rigid Raider:
If they are not doing it for hire or reward, and everyone goes on walks on a voluntary basis I don't see that it's any different from the climbing situation where a bunch of friends go climbing. They don't normally take out insurance.
Those attending are quite capable of making their own ongoing risk assessments like any thing else in life. Eg Do I walk through the woods with overhanging branches that might poke my eye out? Or where there are rabbit holes that might break my leg? Or walk through a field with a bull in it?
I find it difficult to invisage circumstances where a group or group leader can be held liable in such circunstances.
In the case of children or someone with learning difficulties then they should be accompanied by a responsible adult in any event, which is not the group's problem.
So I don't see that insurance is essential. I think we tend to be too paranoud about liability. Walking is almost something everyone does.
Would you take out insurance for walking with your elderly neighbour to the local supermarket every week!? (I'm not talking about car insurance here). Or out with a friend and offering to push her child's buggy for her?