When it comes to doing any work on paths, you need to make sure you think about health and safety. And that's not just the health and safety of contractors and volunteers who might be doing actual practical work, but also that of anyone who might pass by whilst the work is taking place.
There are a lot of regulations which apply to managing health and safety, including the Health and Safety at Work Act 1974, the Manual Handling Operations Regulations 1992 and the Construction (Design and Management) Regulations 2007 amongst others.
Even if you are just doing small tasks with a group of volunteers, you should make sure you have adequate insurance in place and have undertaken a risk assessment of the task before you begin (see the Health and Safety Executive (HSE) website for guidance on doing a risk assessment). You should also make sure that your volunteers know how to use any tools, including the safest way to store and carry the tools at the site.
If you're undertaking a larger construction project, then you'll need to read up on the relevant health and safety legislation. All the regulations have guidance notes or approved codes of practice which you can find on the HSE website. There's also further information on health and safety in the Lowland Paths Guide.