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cheers @chrislybear thanks for dropping in, yes a wonderful place full of treasure. Thanks for your interesting question. I shall try to explain.

In the UK there are criminal laws and "laws of tort", which are nor criminal but civil laws.

So if the police caught you inside or exiting the place and you have not committed a criminal act once inside (theft damage as examples), nor have you say smashed a window to get in then they are powerless to do anything. Trespass is not in itself a criminal offence.

And as a criminal act has not taken place you do not even have to give them your details!

That I hope answers your question.

I have done a lot of this activity across Berlin and the former GDR, but haven't a clue what would have happened if the police turned up. Living life on the edge LOL

Thank you for the explanation! In Germany (from the experience of friends) it really depends on the officer who caught you. If they really want to get you in trouble they can. But most of the time if you are nice and show them that you only took photos they "only" give you a warning. But I have no clue how strict the GDR was, or how it's actually in Berlin. I am mostly in the western part of germany :D

Ok, cheers, handy to know