Surveillance is covert when it is done without the subject being aware it is, or could be, taking place.
Highly skilled Surveillance Officers carry out this work.
Like all of our activities, physical surveillance is carried out in accordance with the law, in particular the Intelligence and Security Act which provides for intelligence warrants that would be required before a Surveillance Officer is able to undertake activities which would otherwise be unlawful.
There is also a Ministerial Policy Statement on conducting surveillance in a public place and another that sets out in more detail certain exemptions Surveillance Officers have from road user rules in order to carry out their work.