Freedom to Photograph
There are still some members of the public who believe that it is illegal to take pictures in a public place. If you are challenged you may consider this a suitable response,
"It is perfectly legal for me to take pictures in a public space and the new data protection act (GDPR) is not applicable to me as I am not using these images to record, learn or decide something about the individuals in the picture. If you still think I’m acting unlawfully, you should call the police immediately".
However, caution must be exercised where children or sensitive establishments are involved.
With respect to taking pictures on private property, you must first seek the permission of the owner. The railways have their own guidelines,
National Rail - Guidelines for Rail Enthusiasts
Last Updated, 16/02/2019