Oops, thanks for pointing that out - we'll be in touch with the Forestry Commission immediately, and hopefully the agreement will be renewed. We have a good working relationship with the FC NF, so there should be no problems there.
As far as I know, there'll be no changes to the agreement due to National Park status.
The agreement covers all land that comprises part of the New Forest, regardless of how that land is used.
Provided your cache meets the conditions of the agreement then you shouldn't have any problems. When a new cache in the Forest is approved by the geocaching.com reviewers, they pass the details to me, I double-check for anything that the FC might not be happy with and then pass the information on to them. If you placed a cache there and it was approved, then if I spotted any possible problem I'd contact you directly before passing the information on, to give you the opportunity of rectifying matters.
I think you can safely assume that the agreement will be renewed shortly, and you can go ahead with your cache. If you have any further questions about it feel free to contact me through my profile.
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Bill, Chairman GAGB
Do not go gentle into that good night.
Rage, rage against the dying of the light. (Dylan Thomas)