The Inland Waterways Association can provide more information. There is an annual inland waterways boat show, and they have a presence at the London boat show. Buoyancy aids are sensible for younger participants and non-swimmers. For older participants a life ring, rope and lookout may be adequate. There is normally more risk of getting trapped between the boat and bank, or from the propeller, than from drowning.
Locks can be particularly dangerous with large drops, deep water and heavy machinery.
Canal water is never clean, and you should be aware of Wiels disease. Be aware that the bilges need pumping regularly to remove water, and more importantly cooking gas and fuel vapour leaks. These activities are probably only for older Scouts and above. It can be a half-one day activity or part of a longer camp. There are various professional centres, or you may be lucky enough to find a parent with a boat.