I'm a fully paid up member but I get your point. You are free to photograph in most NT properties for personal use only but have to get a licence for commercial use. I don't know what the rules are for the Lake District and all the other land and coastline they own.
That's quite right, they will even allow out of hours photo sessions ( none commercial ) for keen photographers. This involves communicating with the National Trust

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Most of the photos I post on this site were taken in Trust properties. ( During normal hours ).
There's an increasingly good GF cake selection in the Trust cafes.
If you ever get p****d of with the English National Trust join the Scottish National Trust: Membership is cheaper & they have a reciprocal agreement which will get you into all English NT properties. ( Thanks to my Uncle Ron for that one ).
Dave, I think you've got some really good BW conversions waiting to be made from those images.