Public Liability Insurance is usually set at £5,000,000 for Forest School Activities. This is the limit required by partnering with organisations such as the Woodland Trust to use their sites. There are different conditions and ranges of cover depending on what activities are carried out. For example limits are set on tree climbing height, water play depths all of which can be excluded or reduced to lower the premium.
Note that there appears to be providers that regularly use sites without the permission of the land owner which therefore invalidates their insurance. This may lead to cancellation of their policy by the insurance company and subsequently leave you exposed should litigation occur.
Get an up to date copy of Forest School Providers Public Liability Insurance and note the expiry date. This is when you’ll need to seek an up to date copy if one is not forthcoming.
Examine the scope of the policy and compare it with the proposed activities including height for climbing, depth for water play, use of rope swings, fire use, tool use, etc.
If you have concerns about other external practices by the provider invalidating the insurance then seek verification from the insurance company to determine the level of insurance currently held.