You can take pictures indoors without flash but the policy is now dependent on the property manager. So every property will be different. Still for this blog it's likely to see more photos given my self editing powers are naff and OC will be demanding to see inside!!
The National Trust already insists that all photos taken on its property are copyright the National Trust and can not be used for commercial purposes. The Trust also has some odd wording in its competition rules e.g
If you submit any material to us, you agree to grant The National Trust a perpetual, royalty-free, worldwide, non-exclusive licence to use your contribution in all media. This includes the right to copy, edit, publish, grant sub-licences and exercise all other copyright and publicity rights over the material. If you do not want to grant these rights, please do not submit your contribution to us.
It does seem that the trust may be reviewing some of the above as well.
The rules on flash are, according to a Trust spokesman, because it is known to have an effect on the retina of the eye that can be 'irritating' for other visitors. I'm not sure if I agree with that but fair enough. Some properties will be unphotographable with out flash e.g. Snowshill Nikon D3s anyone?
The reason for the trusts leaving it to the discretion of the property manager is that some properties have collections not owned by the trust. The Trust will also stop photos if there is a bottleneck.
They are also being flexible on tripods!! Frankly I'd ban them as they will clutter up the place and create a blockage.
I wonder if Ickworth allows photos indoors? or Melford Hall or Anglessey Abbey? or ? Easter should be fun !!