the council has put non alarmed scaffolding on our flats and I have already seen a strange man climbing up. Will my insurance still be valid if a thief uses the scaffolding to break into my home?
~~Your insurance would cover you if anyone broke in, unless you set it up yourself (you didn't) so you have no control and insurance would cover this.~~
Does your insurance have a 'warrant' about scaffolding requiring an alarm, or your flat requiring an alarm? If not, no. Lock your windows.